Fix a couple doc comment typos (#1302)

Author: nex3

lib/src/ast/sass/expression/string.dart

@@ -71,8 +71,8 @@ class StringExpression implements Expression {
     return buffer.interpolation(text.span);
   }
 
-  /// Writes to [buffer] the contents of a string (without quotes) that evalutes
-  /// to [text] according to Sass's parsing logic.
+  /// Writes to [buffer] the contents of a string (without quotes) that
+  /// evaluates to [text] according to Sass's parsing logic.
   ///
   /// This always adds an escape sequence before [quote]. If [static] is true,
   /// it also escapes any `#{` sequences in the string.

lib/src/configuration.dart

@@ -77,7 +77,7 @@ class Configuration {
       ")";
 }
 
-/// A [Configuratoin] that was created with an explicit `with` clause of a
+/// A [Configuration] that was created with an explicit `with` clause of a
 /// `@use` rule.
 ///
 /// Both types of configuration pass through `@forward` rules, but explicit