Cache travis dependencies

Author: mhallin

.travis.yml

@@ -1,4 +1,5 @@
 language: rust
+cache: cargo
 
 rust:
   - stable
@@ -11,8 +12,17 @@ matrix:
 
 script:
   - cargo build --verbose
-  - cargo build --features iron-handlers --verbose
+  - cargo build --verbose --release
+
+  - cargo build --verbose --features iron-handlers
+  - cargo build --verbose --features iron-handlers --release
+
   - cargo test --verbose --features iron-handlers
+  - cargo test --verbose --features iron-handlers --release
+
+before_cache:
+  rm -rf target/debug/juniper*
+  rm -rf target/release/juniper*
 
 after_success: |
   if [ "$TRAVIS_BRANCH" = master -a "$TRAVIS_PULL_REQUEST" = false -a "$TRAVIS_RUST_VERSION" = stable ]; then