fix spelling in core libraries

sdk/lib/io/platform_impl.dart

Index: sdk/lib/io/platform_impl.dart
diff --git a/sdk/lib/io/platform_impl.dart b/sdk/lib/io/platform_impl.dart
index 8b83fc0d8f1d637c35f22b44769a1d42ac67821d..5743b9ef0684f6e9142b53246c587c76161b2888 100644
--- a/sdk/lib/io/platform_impl.dart
+++ b/sdk/lib/io/platform_impl.dart
@@ -22,7 +22,7 @@ class _Platform {
    * a non-empty name and a value separated by a '=' character.
    * The name does not contain a '=' character,
    * so the name is everything up to the first '=' character.
-   * Values are everything after the first '=' charcacter.
+   * Values are everything after the first '=' character.
    * A value may contain further '=' characters, and it may be empty.
    *
    * Returns an [OSError] if retrieving the environment fails.
@@ -38,7 +38,7 @@ class _Platform {
   static String packageRoot = _packageRoot();
   static String packageConfig = _packageConfig();
 
-  // Cache the OS environemnt. This can be an OSError instance if
+  // Cache the OS environment. This can be an OSError instance if
   // retrieving the environment failed.
   static var/*OSError|Map<String,String>*/ _environmentCache;