Fix spawn reference return

Author: alexheretic

lib/index.js

@@ -329,7 +329,7 @@ class RustLanguageClient extends AutoLanguageClient {
     return checkToolchain(this.busySignalService)
       .then(toolchain => checkRls(this.busySignalService).then(() => toolchain))
       .then(toolchain => {
-        cp.spawn("rustup", ["run", configToolchain(), "rls"], { env: serverEnv(toolchain) })
+        return cp.spawn("rustup", ["run", configToolchain(), "rls"], { env: serverEnv(toolchain) })
       })
   }
 }