Exclude /target instead of serde_type.rs

`kcov`'s option `--exclude-pattern` takes a _path_, not a regex:
```
    --exclude-path=P1[,P2...]
          Comma-separated list of paths to exclude from the report.

    --exclude-pattern=P1[,P2...]
          Comma-separated list of path patterns to exclude from the report.
```

.travis.yml

@@ -53,4 +53,4 @@ after_success:
   # https://github.com/huonw/travis-cargo/issues/58
   # See https://github.com/ujh/iomrascalai/blob/master/.travis.yml
   - if [[ "$TRAVIS_OS_NAME" == "linux" && "$TRAVIS_RUST_VERSION" == "stable" ]]; then travis-cargo coveralls --no-sudo --verify; fi
-  - if [[ "$TRAVIS_OS_NAME" == "linux" && "$TRAVIS_RUST_VERSION" == "stable" ]]; then ./kcov/build/src/kcov --verify --coveralls-id=$TRAVIS_JOB_ID --exclude-pattern=/.cargo,serde_type.rs target/kcov target/debug/gitlab_api-*; fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" && "$TRAVIS_RUST_VERSION" == "stable" ]]; then ./kcov/build/src/kcov --verify --coveralls-id=$TRAVIS_JOB_ID --exclude-pattern=/.cargo,/target target/kcov target/debug/gitlab_api-*; fi