CI: Bump minimum supported Rust version to 1.34.2

.appveyor.yml

   matrix:
     - channel: nightly
       target: x86_64-pc-windows-msvc
-      cargoflags: --no-default-features
     - channel: nightly
       target: x86_64-pc-windows-gnu
-      cargoflags: --no-default-features
     - channel: nightly
       target: i686-pc-windows-gnu
-      cargoflags: --no-default-features
     - channel: stable
       target: x86_64-pc-windows-msvc
-      cargoflags: --no-default-features
     - channel: stable
       target: i686-pc-windows-msvc
-      cargoflags: --no-default-features
-    - channel: 1.27.2
+    - channel: 1.34.2
       target: x86_64-pc-windows-msvc
 
 install:
 
 test_script:
   - cargo test --verbose
-  - cargo test --verbose %cargoflags%
+  - cargo test --verbose --no-default-features

.travis.yml

   - stable
   - beta
   - nightly
-  - 1.27.2
+  - 1.34.2
 script:
   - |
-      if [ "$TRAVIS_RUST_VERSION" == "1.27.2" ]; then
-        cargo test --verbose;
-        cargo doc --verbose --no-deps;
-      else
-        cargo test --verbose;
-        cargo test --verbose --no-default-features;
-        cargo doc --verbose;
-      fi
+      cargo test --verbose;
+      cargo test --verbose --no-default-features;
+      cargo doc --verbose;