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/DocsLayout.js

@@ -16,7 +16,8 @@ const DocsSidebar = require('./DocsSidebar.js');
 const OnPageNav = require('./nav/OnPageNav.js');
 const Site = require('./Site.js');
 const translation = require('../server/translation.js');
-const {idx} = require('./utils.js');
+const docs = require('../server/docs.js');
+const {idx, getGitLastUpdated} = require('./utils.js');
 
 // component used to generate whole webpage for docs, including sidebar/header/footer
 class DocsLayout extends React.Component {
@@ -43,6 +44,12 @@ class DocsLayout extends React.Component {
     if (this.props.Doc) {
       DocComponent = this.props.Doc;
     }
+    let updateTime;
+    if (this.props.config.enableUpdateTime) {
+      const filepath = docs.getFilePath(metadata);
+      updateTime = getGitLastUpdated(filepath);
+    }
+
     const title =
       idx(i18n, ['localized-strings', 'docs', id, 'title']) || defaultTitle;
     const hasOnPageNav = this.props.config.onPageNav === 'separate';
@@ -100,6 +107,13 @@ class DocsLayout extends React.Component {
                 </a>
               )}
             </div>
+            {this.props.config.enableUpdateTime &&
+              updateTime && (
+                <p style={{fontSize: '12px', textAlign: 'right'}}>
+                  <strong>Last updated: </strong>
+                  {updateTime}
+                </p>
+              )}
           </Container>
           {hasOnPageNav && (
             <nav className="onPageNav">