Update pretty_time methods import path

Updates path for pretty time related methods
to import from `datetime_utility.js`

app/assets/javascripts/sidebar/components/time_tracking/collapsed_state.vue

 <script>
   import { __, sprintf } from '~/locale';
-  import { abbreviateTime } from '~/lib/utils/pretty_time';
+  import { abbreviateTime } from '~/lib/utils/datetime_utility';
   import icon from '~/vue_shared/components/icon.vue';
   import tooltip from '~/vue_shared/directives/tooltip';
 

app/assets/javascripts/sidebar/components/time_tracking/comparison_pane.vue

 <script>
-import { parseSeconds, stringifyTime } from '../../../lib/utils/pretty_time';
+import { parseSeconds, stringifyTime } from '~/lib/utils/datetime_utility';
 import tooltip from '../../../vue_shared/directives/tooltip';
 
 export default {