Fix 'Cannot assign to 'level' because it is a constant or a read-only…

… property.'

```
src/client.ts:186:10 - error TS2540: Cannot assign to 'level' because it is a constant or a read-only property.

186   logger.level = process.env.LOG_LEVEL || 'warn';
             ~~~~~

make: *** [Makefile:14: compile] Error 2
```

See microsoft/TypeScript#6751 (comment)
and https://stackoverflow.com/questions/38818475/left-hand-side-of-assignment-expression-cannot-be-a-constant-or-a-read-only-prop/38833920#38833920

distribution/client/src/client.ts

@@ -183,7 +183,7 @@ if (require.main === module) {
    * Allow the log level to be overridden in the environment for debugging
    * purposes by the user
    */
-  logger.level = process.env.LOG_LEVEL || 'warn';
+  (logger as any).level = process.env.LOG_LEVEL || 'warn';
   /* Main entrypoint for module */
   UI.publish('Starting the evergreen-client..', { log: 'info' });
   const client = new Client();