Revert "Remove handling of below node 8"

This reverts commit f41de4c.

errors/old-node-version.md

@@ -0,0 +1,10 @@
+# Old Node Version
+
+#### Why This Error Occurred
+
+In order to execute code that contains the `async` or `await` keywords, you need to have at least version 8.0.0 of [Node.js](https://nodejs.org/en/) installed on the device that runs `micro`. If that's not the case, you will see this error.
+
+#### Possible Ways to Fix It
+
+- Ensure that at least version 8.0.0 of [Node.js](https://nodejs.org/en/) is installed
+- [Transpile](https://github.com/zeit/micro#transpilation) the code of your microservice

lib/handler.js

@@ -12,6 +12,18 @@ module.exports = async file => {
 		}
 	} catch (err) {
 		logError(`Error when importing ${file}: ${err.stack}`, 'invalid-entry');
+
+		if (
+			err instanceof SyntaxError &&
+      /\s+async\s+/.test(err.stack) &&
+      Number(process.versions.node.split('.')[0]) < 8
+		) {
+			logError(
+				'In order for `async` & `await` to work, you need to use at least Node.js 8!',
+				'old-node-version'
+			);
+		}
+
 		process.exit(1);
 	}