Provide realpath for module resolvution in LSHost

Author: Andy Hanson

src/server/editorServices.ts

@@ -113,7 +113,8 @@ namespace ts.server {
             this.moduleResolutionHost = {
                 fileExists: fileName => this.fileExists(fileName),
                 readFile: fileName => this.host.readFile(fileName),
-                directoryExists: directoryName => this.host.directoryExists(directoryName)
+                directoryExists: directoryName => this.host.directoryExists(directoryName),
+                realpath: path => this.host.realpath(path)
             };
         }