Fix references to https://sites.google.com/site/skiadocs/.
Point them to their equivalent in https://skia.org.
BUG=None
R=hcm@google.com, jcgregorio@google.com
NOTRY=true
Review URL: https://codereview.chromium.org/856353004
diff --git a/skia.gyp b/skia.gyp
index e554df1..2205de1 100644
--- a/skia.gyp
+++ b/skia.gyp
@@ -6,7 +6,7 @@
# More targets are defined within the gyp/ directory, but those are
# not intended for external use and may change without notice.
#
-# Full documentation at https://sites.google.com/site/skiadocs/
+# Full documentation at https://skia.org.
#
{
'targets': [