Fix a trivial typo and remove redundancy (#93)

Author: kinow

oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java

@@ -181,7 +181,7 @@ private boolean shouldRefresh() {
   public AccessToken refreshAccessToken() throws IOException {
     throw new IllegalStateException("OAuth2Credentials instance does not support refreshing the"
         + " access token. An instance with a new access token should be used, or a derived type"
-        + " that supports refreshing should be used.");
+        + " that supports refreshing.");
   }
 
   /**

oauth2_http/java/com/google/auth/oauth2/ServiceAccountCredentials.java

@@ -275,7 +275,7 @@ public static ServiceAccountCredentials fromStream(InputStream credentialsStream
   @Override
   public AccessToken refreshAccessToken() throws IOException {
     if (createScopedRequired()) {
-      throw new IOException("Scopes not configured for service account. Scoped should be specifed"
+      throw new IOException("Scopes not configured for service account. Scoped should be specified"
           + " by calling createScoped or passing scopes to constructor.");
     }