remove useless usePipenv local vars & document the option

Author: dschep

README.md

@@ -35,9 +35,14 @@ custom:
 This must be the full image name and tag to use, including the runtime specific tag if applicable.
 
 ## Pipenv support :sparkles::cake::sparkles:
-If you include a `Pipfile` and have `pipenv` installed instead of a
-`requirements.txt` this will use `pipenv lock --r` to generate
-them. It is fully compatible with all options such as `zip` and `dockerizePip`.
+If you include a `Pipfile` and have `pipenv` installed instead of a `requirements.txt` this will use
+`pipenv lock --r` to generate them. It is fully compatible with all options such as `zip` and
+`dockerizePip`. If you don't want this plugin to generate it for you, set the following option:
+```yaml
+custom:
+  pythonRequirements:
+    usePipenv: false
+```
 
 
 ## Dealing with Lambda's size limitations

lib/pip.js

@@ -8,8 +8,7 @@ const {spawnSync} = require('child_process');
  */
 function installRequirements() {
   let fileName = this.options.fileName;
-  let usePipenv = this.options.usePipenv;
-  if (usePipenv && fse.existsSync(path.join(this.servicePath, 'Pipfile'))) {
+  if (this.options.usePipenv && fse.existsSync(path.join(this.servicePath, 'Pipfile'))) {
     fileName = '.serverless/requirements.txt';
   }
 

lib/pipenv.js

@@ -7,8 +7,7 @@ const {spawnSync} = require('child_process');
   * @return {Promise}
   */
 function pipfileToRequirements() {
-  let usePipenv = this.options.usePipenv;
-  if (!usePipenv || !fse.existsSync(path.join(this.servicePath, 'Pipfile')))
+  if (!this.options.usePipenv || !fse.existsSync(path.join(this.servicePath, 'Pipfile')))
     return;
 
   this.serverless.cli.log('Generating requirements.txt from Pipfile...');