Ensure that mono --assembly-loader flag is passed

Author: DustinCampbell

src/omnisharp/launcher.ts

@@ -272,6 +272,7 @@ function launchNixMono(launchPath: string, cwd: string, args: string[]): Promise
     return canLaunchMono()
         .then(() => {
             let argsCopy = args.slice(0); // create copy of details args
+            argsCopy.unshift("--assembly-loader=strict");
             argsCopy.unshift(launchPath);
 
             let process = spawn('mono', argsCopy, {