Fix erroneous use of 'schema' instead of 'scheme'

requests/exceptions.py

@@ -80,11 +80,11 @@ class TooManyRedirects(RequestException):
 
 
 class MissingSchema(RequestException, ValueError):
-    """The URL schema (e.g. http or https) is missing."""
+    """The URL scheme (e.g. http or https) is missing."""
 
 
 class InvalidSchema(RequestException, ValueError):
-    """See defaults.py for valid schemas."""
+    """The URL scheme provided is either invalid or unsupported."""
 
 
 class InvalidURL(RequestException, ValueError):

requests/models.py

@@ -386,7 +386,7 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
             raise InvalidURL(*e.args)
 
         if not scheme:
-            error = ("Invalid URL {0!r}: No schema supplied. Perhaps you meant http://{0}?")
+            error = ("Invalid URL {0!r}: No scheme supplied. Perhaps you meant http://{0}?")
             error = error.format(to_native_string(url, 'utf8'))
 
             raise MissingSchema(error)