Prebuild inkwell and run tests in release to hopefully not take as long

Author: TheDan64

.travis.yml

@@ -24,7 +24,8 @@ include_base: &BASE
     - export LLVM_PATH=/usr/share/llvm-${LLVM_VERSION}/cmake/
     - sed -i -e 's/llvm-sys = ".*"/llvm-sys = "'${LLVM_VERSION_SHORT}'"/' Cargo.toml
   script:
-    - cargo test --no-default-features --features "llvm${LLVM_VERSION_DASH}" --verbose
+    - cargo build --release
+    - cargo test --no-default-features --features "llvm${LLVM_VERSION_DASH}" --verbose --release
 
 matrix:
   allow_failures: