Do release builds on Travis-CI and AppVeyor

(Since we may upload artifacts.)

Author: danieldk

.appveyor.yml

@@ -11,7 +11,7 @@ install:
   - cargo install pyo3-pack
 
 build_script:
-- pyo3-pack build
+- pyo3-pack build --release
 
 artifacts:
   - path: '**/*.whl'

.travis.yml

@@ -37,8 +37,8 @@ install:
   - rustup component add rustfmt
 
 script:
-  - pyo3-pack build
   - cargo fmt --all -- --check
+  - pyo3-pack build --release
 deploy:
   provider: releases
   api_key: