Update toc time for 1.15

Author: VesaJuvonen

docs/toc.yml

@@ -458,7 +458,7 @@
     items:
     - name: Overview
       href: spfx/roadmap.md
-    - name: SPFx v1.15 - April 19, 2022
+    - name: SPFx v1.15 - June 1, 2022
       href: spfx/release-1.15.md      
     - name: SPFx v1.14 - February 17, 2022
       href: spfx/release-1.14.md