disable stable rustc ci

Author: alecmocatta

azure-pipelines.yml

@@ -12,7 +12,7 @@ jobs:
 - template: rust.yml@templates
   parameters:
     default:
-      rust_toolchain: stable nightly
+      rust_toolchain: nightly
       rust_lint_toolchain: nightly-2019-07-19
       rust_flags: ''
       rust_features: ''