chore(AIP-129): trim trailing space (#1271)

Author: TheApX

aip/general/0129.md

@@ -67,7 +67,7 @@ field's name.
 
 For user-specified fields, the value in response from the service **must** be
 the same as provided by the create or update request. For string fields this
-means returning the value unchanged, with one exception: 
+means returning the value unchanged, with one exception:
 
 * When a string field has a data type annotation, a normalized string that
   represents the given value **may** be returned.