[beta] Boostrap from released compilers

No need to use dev any more!

Author: alexcrichton

src/stage0.txt

@@ -12,7 +12,7 @@
 # source tarball for a stable release you'll likely see `1.x.0` for rustc and
 # `0.x.0` for Cargo where they were released on `date`.
 
-date: 2017-08-27
+date: 2017-08-31
 rustc: 1.20.0
 cargo: 0.21.0
 
@@ -34,4 +34,4 @@ cargo: 0.21.0
 # looking at a beta source tarball and it's uncommented we'll shortly comment it
 # out.
 
-dev: 1
+#dev: 1