Check LOGGING env-var for "true" (microsoft#78)

LOGGING env var should be exlicitly set to "true", in order to log
requests.

Currently it just needs to be truethy, which doesn't correspond with the
the current default value in the example .env.local file (where it's
"false").
Explicit "true" is also how other env-vars are checked, eg
https://github.com/microsoft/code-push-server/blob/08e97d751620ad7867bb0c9b94633e94f2c01c68/api/script/default-server.ts#L110

Author: grav

api/script/default-server.ts

@@ -90,7 +90,7 @@ export function start(done: (err?: any, server?: express.Express, storage?: Stor
         next();
       });
 
-      if (process.env.LOGGING) {
+      if (process.env.LOGGING === "true") {
         app.use((req: express.Request, res: express.Response, next: (err?: any) => void): any => {
           console.log(); // Newline to mark new request
           console.log(`[REST] Received ${req.method} request at ${req.originalUrl}`);