Make sure that LF line endings are also used on Windows

R=mathias@chromium.org

Bug: v8:7775
Change-Id: I5a8d100969f47a1768be1ed8098535c0c66434a3
Reviewed-on: https://chromium-review.googlesource.com/1102322
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53753}

.gitattributes

 # Automatically normalize line endings (to LF) for all text-based files.
-* text=auto
+* text=auto eol=lf