Switch Windows CI builds from windows-gnu to windows-msvc.

The Travis default of windows-gnu suffers from rust-lang/rust#47048, I
think. I don't see an easy way to address this right now, but switching
our Windows builds to windows-msvc will avoid this and is more realistic
target anyway.

.travis.yml

@@ -7,23 +7,24 @@ os:
   - linux
   - osx
   - windows
-  
+
 env:
   matrix:
     - RELEASE=
     - RELEASE=--release
 
-before_script:
-# rustfmt may not always be available in nightly
-- if [[ "$TRAVIS_RUST_VERSION" != *nightly* ]]; then rustup component add rustfmt; fi
+install:
+  # rustfmt may not always be available in nightly
+  - if [[ "$TRAVIS_RUST_VERSION" != *nightly* ]]; then rustup component add rustfmt; fi
+  - if [[ "$TRAVIS_OS_NAME" == "windows" ]]; then T=x86_64-pc-windows-msvc; rustup target add $T; TARGET=--target=$T; fi
 
 script:
   # We cannot run `cargo test` with the mp4parse_fallible feature enabled
   # (see comment where the feature is defined in mp4parse_capi/Cargo.toml),
   # but we can at least check for changes behind features that would break the
   # build.
   - cargo check --all --verbose $RELEASE --tests --all-features
-  - cargo test --all --verbose $RELEASE
+  - cargo test --all --verbose $RELEASE $TARGET
   - cargo doc --package mp4parse_capi
   # The `false` after `echo` is necessary to avoid false negatives due to `echo` returning success
   - if [[ "$TRAVIS_RUST_VERSION" != *nightly* ]]; then cargo fmt -- --check || (echo "Please reformat your code with 'cargo fmt' (version $(cargo fmt -- --version))"; false); fi