Include the external/ folder in the coverage report for gulp unittestcli

Given that the (browser) `gulp unittest` coverage includes the `external/` folder, it seems reasonable to include that folder in the coverage report when running unit-tests in Node.js as well.

Author: Snuffleupagus

.c8rc.json

@@ -1725,7 +1725,7 @@ function buildLibHelper(bundleDefines, inputStream, outputDir) {
           "babel-plugin-istanbul",
           {
             cwd: __dirname,
-            include: ["src/**/*.js", "web/**/*.js"],
+            include: ["external/**/*.js", "src/**/*.js", "web/**/*.js"],
           },
         ]);
       }