doc: minor grammatical update

Per: nodejs/node-v0.x-archive#9009

Originally submitted by @peerwit

Reviewed By: Sakthipriyan Vairamani <[email protected]>
PR-URL: #2378

Author: jasnell

doc/api/crypto.markdown

@@ -135,7 +135,7 @@ Returned by `crypto.createHash`.
 
 Updates the hash content with the given `data`, the encoding of which
 is given in `input_encoding` and can be `'utf8'`, `'ascii'` or
-`'binary'`.  If no encoding is provided and the input is a string an
+`'binary'`.  If no encoding is provided, and the input is a string, an
 encoding of `'binary'` is enforced. If `data` is a `Buffer` then
 `input_encoding` is ignored.