Add skia.conf (configuration file that supports printShaders, etc...) to .gitignore

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1734563003

Review URL: https://codereview.chromium.org/1734563003
diff --git a/.gitignore b/.gitignore
index e7d565c..3239f42 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,6 +23,7 @@
 platform_tools/chromeos/third_party/externals
 platform_tools/chromeos/toolchain
 /skps
+skia.conf
 third_party/externals
 tools/skp/page_sets/data/*.json
 tools/skp/page_sets/data/*.wpr