Fix "rust.rls.args", "rust.rls.env" (#291)

* Consider "rust.rls.executable" when determining args

* Fix "rust.rls.env"

Author: KalitaAlexey

src/components/configuration/RlsConfiguration.ts

@@ -44,7 +44,9 @@ export class RlsConfiguration {
      * Returns arguments for RLS
      */
     public getArgs(): string[] {
-        if (this._rustup && this._rustup.isRlsInstalled()) {
+        // When the user specifies some executable path, the user expects the extension not to add
+        // some arguments
+        if (this._executableUserPath === undefined && this._rustup && this._rustup.isRlsInstalled()) {
             return ['run', 'nightly', 'rls'].concat(this._userArgs);
         } else {
             return this._userArgs;
@@ -55,7 +57,7 @@ export class RlsConfiguration {
      * Returns environment to run RLS in
      */
     public getEnv(): object {
-        const env = Object.create(this._userEnv);
+        const env: any = Object.assign({}, this._userEnv);
         if (!env.RUST_SRC_PATH) {
             const rustSourcePath = this._rustSource.getPath();
             if (rustSourcePath) {