Correct documentation in `Parser`.

Removed a trailing `in` from the final line which caused a compilation
error. [skip ci]

Reviewed by: thomie

Differential Revision: https://phabricator.haskell.org/D744

compiler/parser/Parser.y

@@ -28,7 +28,7 @@
 --       filename = "\<interactive\>"
 --       location = mkRealSrcLoc (mkFastString filename) 1 1
 --       buffer = stringToStringBuffer str
---       parseState = mkPState flags buffer location in
+--       parseState = mkPState flags buffer location
 -- @
 module Parser (parseModule, parseImport, parseStatement,
                parseDeclaration, parseExpression, parseTypeSignature,