docs: Update Readme, package is singular (#228)

The package referred to in each Readme.md is singular.

Author: seebees

modules/cache-material/README.md

@@ -4,7 +4,7 @@ The AWS Encryption SDK for JavaScript is a client-side encryption library design
 
 ## About @aws-crypto/cache-material
 
-This packages is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
+This package is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
 
 ## License
 

modules/kms-keyring/README.md

@@ -4,7 +4,7 @@ The AWS Encryption SDK for JavaScript is a client-side encryption library design
 
 ## About @aws-crypto/kms-keyring
 
-This packages is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
+This package is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
 
 ## License
 

modules/material-management/README.md

@@ -4,7 +4,7 @@ The AWS Encryption SDK for JavaScript is a client-side encryption library design
 
 ## About @aws-crypto/material-management
 
-This packages is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
+This package is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
 
 ## License
 

modules/raw-keyring/README.md

@@ -4,7 +4,7 @@ The AWS Encryption SDK for JavaScript is a client-side encryption library design
 
 ## About @aws-crypto/raw-keyring
 
-This packages is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
+This package is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
 
 ## License
 

modules/serialize/README.md

@@ -4,7 +4,7 @@ The AWS Encryption SDK for JavaScript is a client-side encryption library design
 
 ## About @aws-crypto/serialize
 
-This packages is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
+This package is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
 
 ## License
 

modules/web-crypto-backend/README.md

@@ -4,7 +4,7 @@ The AWS Encryption SDK for JavaScript is a client-side encryption library design
 
 ## About @aws-crypto/web-crypto-backend
 
-This packages is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
+This package is not intended for direct use by clients. To get started with the AWS Encryption SDK for JavaScript, follow the instructions in [the README](https://github.com/aws/aws-encryption-sdk-javascript/blob/master/README.md).
 
 ## License