Update lib to std-future

.travis.yml

@@ -15,10 +15,10 @@ addons:
 matrix:
   include:
   - rust: nightly
-  - rust: stable
+#  - rust: stable
     before_deploy: cargo doc --no-deps
-  allow_failures:
-    - rust: nightly
+#  allow_failures:
+#    - rust: nightly
 
 before_script:
   - cargo clean
@@ -39,8 +39,8 @@ script:
   # Run integration tests
   - cargo test -p h2-tests
 
-  # Run h2spec on stable
-  - if [ "${TRAVIS_RUST_VERSION}" = "stable" ]; then ./ci/h2spec.sh; fi
+  # Run h2spec on nightly for the time being. TODO: Change it to stable after Rust 1.38 release
+  - if [ "${TRAVIS_RUST_VERSION}" = "nightly" ]; then ./ci/h2spec.sh; fi
 
   # Check minimal versions
   - if [ "${TRAVIS_RUST_VERSION}" = "nightly" ]; then cargo clean; cargo check -Z minimal-versions; fi