Clarify message "No typescript errors found."

When this message appears in context of webpack-dev-server,
it could be unclear what kind of errors (webpack build vs. typescript).
Sometimes there is a prior "Error checking in progress" message,
but not always, and may be far above the "No errors found."

src/hooks/tap-done-to-async-get-issues.ts

@@ -68,7 +68,7 @@ function tapDoneToAsyncGetIssues(
       // print stats of the compilation
       config.logger.log(statsFormatter(issues, stats));
     } else {
-      config.logger.log(chalk.green('No errors found.'));
+      config.logger.log(chalk.green('No typescript errors found.'));
     }
 
     // report issues to webpack-dev-server, if it's listening