Core/Lint.fs: fix build

Author: webwarrior-ws

src/FSharpLint.Core/Application/Lint.fs

@@ -660,7 +660,7 @@ module Lint =
 
             let lintSingleFile filePath =
                 if IO.File.Exists filePath then
-                    match ParseFile.parseFile filePath checker None with
+                    match ParseFile.parseFile filePath checker None |> Async.RunSynchronously with
                     | ParseFile.Success astFileParseInfo ->
                         let parsedFileInfo =
                             { Source = astFileParseInfo.Text