Fix a typo in the doc string

MaybeRaise in lib/errors.py had a typo in the doc string

Signed-off-by: René Nussbaumer <rn@google.com>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/errors.py

@@ -304,7 +304,7 @@ def EncodeException(err):
 
 
 def MaybeRaise(result):
-  """Is this looks like an encoded Ganeti exception, raise it.
+  """If this looks like an encoded Ganeti exception, raise it.
 
   This function tries to parse the passed argument and if it looks
   like an encoding done by EncodeException, it will re-raise it.