fix typo in .gitignore

R=franzih@chromium.org, kozyatinskiy@chromium.org, machenbach@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2540323003
Cr-Commit-Position: refs/heads/master@{#41406}

.gitignore

@@ -67,7 +67,7 @@ shell_g
 /third_party/icu
 /third_party/instrumented_libraries
 /third_party/inspector_protocol
-/third_party/jinga2
+/third_party/jinja2
 /third_party/llvm
 /third_party/llvm-build
 /third_party/markupsafe