bump version in ui/config and datestamp release notes

Author: Dottenpixel

RELEASENOTES.general.md

@@ -1,7 +1,7 @@
 <!-- Release notes authoring guidelines: http://keepachangelog.com/ -->
 <!-- On release, add general notes here. In time the legacy release notes will be add to this -->
 
-## 2.15.0 - Upcoming
+## 2.15.0 - March 25, 2020
 
 - Removed Salesforce Sans as the default typeface and replaced it with OS-specific defaults.
 - Updated many of our design tokens and other colors to utilize the new Salesforce Color System. For more information, [read our article on Medium about this system](https://medium.com/salesforce-ux/the-salesforce-color-system-c7c6b5b9c577).

RELEASENOTES.md

@@ -1,7 +1,7 @@
 <!-- Release notes authoring guidelines: http://keepachangelog.com/ -->
 <!-- !!! THIS FILE IS AUTO-GENERATED !!! DO NOT EDIT THIS FILE MANUALLY !!! -->
 
-## Release 2.15.0 - Upcoming
+## Release 2.15.0 - March 25, 2020
 
 - Removed Salesforce Sans as the default typeface and replaced it with OS-specific defaults.
 - Updated many of our design tokens and other colors to utilize the new Salesforce Color System. For more information, [read our article on Medium about this system](https://medium.com/salesforce-ux/the-salesforce-color-system-c7c6b5b9c577).

ui/_config.scss

@@ -9,7 +9,7 @@
 ///
 /// @type String
 /// @access private
-$app-version: "2.14.3";
+$app-version: "2.15.0";
 
 /// Debug mode (uncomment to activate)
 /// Turn on to output deprecation warnings during development