Merge pull request rust-lang#36602 from brson/beta-next

Bump to beta.4

Author: brson

mk/main.mk

@@ -18,7 +18,7 @@ CFG_RELEASE_NUM=1.12.0
 # An optional number to put after the label, e.g. '.2' -> '-beta.2'
 # NB Make sure it starts with a dot to conform to semver pre-release
 # versions (section 9)
-CFG_PRERELEASE_VERSION=.3
+CFG_PRERELEASE_VERSION=.4
 
 ifeq ($(CFG_RELEASE_CHANNEL),stable)
 # This is the normal semver version string, e.g. "0.12.0", "0.12.0-nightly"