Update bundled gems list at 1500946ce4 [ci skip]

NEWS.md

@@ -37,6 +37,10 @@ The following bundled gems are updated.
 * typeprof 0.21.9
 * debug 1.9.1
 
+The following bundled gem is promoted from default gems.
+
+* mutex_m 0.2.0
+
 See GitHub releases like [GitHub Releases of Logger](https://github.com/ruby/logger/releases) or changelog for details of the default gems or bundled gems.
 
 ## Supported platforms