Add cargo fmt to travis build config

Author: Atul9

.travis.yml

@@ -5,5 +5,12 @@ rust:
   - nightly
 
 script:
+  - |
+    if [[ $TRAVIS_RUST_VERSION == *stable* ]]
+    then
+      rustup component add rustfmt
+      cargo fmt --version
+      cargo fmt -- --check || (echo "Please reformat your code with 'cargo fmt' (version $(cargo fmt --version))"; false)
+    fi
   - cargo build --verbose --all
   - cargo test --verbose --all