fix: local dev env lambda return value

src/lambda.ts

@@ -664,11 +664,13 @@ Previous exit stack: ${this.lastExitStack}`)
       const promise = this.preProcess({ event, context })
         .then(() => this.run())
 
-      if (this.isLocal) return promise
-
-      // until issue is resolved, avoid returning a promise:
-      // https://github.com/aws/aws-xray-sdk-node/issues/27#issuecomment-380092859
-      promise.then(result => context.done(null, result), context.done)
+      if (context.done) {
+        // until issue is resolved, avoid returning a promise:
+        // https://github.com/aws/aws-xray-sdk-node/issues/27#issuecomment-380092859
+        promise.then(result => context.done(null, result), context.done)
+      } else {
+        return promise
+      }
     }
   }