Bootstrap from stable

Author: Mark-Simulacrum

src/ci/channel

@@ -1 +1 @@
-nightly
+beta

src/stage0.txt

@@ -12,14 +12,14 @@
 # stable release's version number. `date` is the date where the release we're
 # bootstrapping off was released.
 
-date: 2021-05-23
-rustc: beta
+date: 2021-06-17
+rustc: 1.53.0
 
 # We use a nightly rustfmt to format the source because it solves some
 # bootstrapping issues with use of new syntax in this repo. If you're looking at
 # the beta/stable branch, this key should be omitted, as we don't want to depend
 # on rustfmt from nightly there.
-rustfmt: nightly-2021-03-25
+# rustfmt: nightly-2021-03-25
 
 # When making a stable release the process currently looks like:
 #