add custom redirect for /en/stablecoins since it is giving a 404 error

Author: pettinarip

public/_redirects

@@ -178,4 +178,6 @@
 
 /studio /en/deprecated-software/#ethereum-studio 301!
 
-/*/studio /:splat/deprecated-software/#ethereum-studio 301!
+/*/studio /:splat/deprecated-software/#ethereum-studio 301!
+
+/en/stablecoins /stablecoins 301!