Fix Travis Windows UI tests

Just using `dos2unix tests/ui/**/*` did not work because the tool was
only transforming the first directory. That's the reason for using
`find`.

Interestingly `find` has precedence rules for its operators, too.

So you have to be careful to add opening/closing braces to denote the
precedence. Example:

```shell
find tests/ui/* -name '*.rs' -or -name '*.stderr' -exec dos2unix '{}' +
```

The above will be interpreted like this:

(find files matching `*.rs`) OR (find files matching `*.stderr` AND exec dos2unix)

which would only execute over the stderr files. That's why the braces are needed:

```shell
find tests/ui/* \( -name '*.rs' -or -name '*.stderr' -or -name '*.stdout' \) -exec dos2unix '{}' +
```

.travis.yml

@@ -40,6 +40,7 @@ install:
       fi
       if [ "$TRAVIS_OS_NAME" == "windows" ]; then
         choco install windows-sdk-10.0
+        find tests/ui/* \( -name '*.rs' -or -name '*.stderr' -or -name '*.stdout' \) -exec dos2unix '{}' +
       fi
     fi