Rust 1.36.0 is now required to build without Cargo.lock

Author: koute

.travis.yml

@@ -40,7 +40,7 @@ jobs:
   include:
     - <<: *test
       os: linux
-      rust: 1.31.0
+      rust: 1.36.0
       env: CHECK_ONLY=1 WITHOUT_CARGO_LOCK=1
     - <<: *test
       os: linux