fix(MongoMemoryReplSet): _initReplSet: throw error if "this.servers.l…

…ength" is "<= 0"

- throw if number is 0 or less, not just falsy

packages/mongodb-memory-server-core/src/MongoMemoryReplSet.ts

@@ -328,7 +328,7 @@ export class MongoMemoryReplSet extends EventEmitter {
       throw new Error('Not in init phase.');
     }
     log('Initializing replica set.');
-    if (!this.servers.length) {
+    if (this.servers.length <= 0) {
       throw new Error('One or more servers are required.');
     }
     const uris = this.servers.map((server) => server.getUri());