fix verifier.verify() docs

Thanks Sitelier. Closes GH-651.

doc/api/crypto.markdown

@@ -118,12 +118,12 @@ This is the mirror of the signing object above.
 
 ### verifier.update(data)
 
-Updates the verifyer object with data.
+Updates the verifier object with data.
 This can be called many times with new data as it is streamed.
 
-### verifier.verify(public_key, signature, signature_format='binary')
+### verifier.verify(cert, signature, signature_format='binary')
 
-Verifies the signed data by using the `public_key` which is a string containing
+Verifies the signed data by using the `cert` which is a string containing
 the PEM encoded public key, and `signature`, which is the previously calculates
 signature for the data, in the `signature_format` which can be `'binary'`, `'hex'` or `'base64'`.