feat: last updated time in docs (#913)

* Adding last updated time for docs

* Making file path general and other suggested changes

* Checking if time returned is null due to absence of git or some other issue

* Adding option to enable/disable update time feature and test-doc

* Adding simple unit tests for getGitUpdateTime()

* nits & rewrote failing test

* consistent test naming

* Adding optional updateEnableTime in documentation

* package-lock & yarn.lock

lib/core/utils.js

@@ -4,6 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  */
+const spawn = require('cross-spawn');
 
 const TRUNCATE_MARKER = /<!--\s*truncate\s*-->/;
 
@@ -32,9 +33,21 @@ function idx(target, path) {
   return path.reduce((obj, key) => obj && obj[key], target);
 }
 
+function getGitLastUpdated(filepath) {
+  const timeSpan = spawn
+    .sync('git', ['log', '-1', '--format=%ct', filepath])
+    .stdout.toString('utf-8');
+  if (timeSpan) {
+    const date = new Date(parseInt(timeSpan, 10) * 1000);
+    return date.toLocaleString();
+  }
+  return null;
+}
+
 module.exports = {
   blogPostHasTruncateMarker,
   extractBlogPostBeforeTruncate,
+  getGitLastUpdated,
   getPath,
   removeExtension,
   idx,