.gitattributes: don't send large binaries to the builders

Fixes golang/go#11199

Change-Id: I8084203b62921f06e8a765b2b2ff4c293e8d67ef
Reviewed-on: https://go-review.googlesource.com/11050
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/.gitattributes b/.gitattributes
index d2f212e..be5533b 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -8,3 +8,14 @@
 # See golang.org/issue/9281
 
 * -text
+
+# The builders assume the git archive *.tar.gz of the tree is under
+# 25 MB but this repo is 31+ MB with all the images.
+# So exclude those.
+# See https://golang.org/issue/11199
+
+*.jpg export-ignore
+*.jpeg export-ignore
+*.png export-ignore
+*.gif export-ignore
+*.pdf export-ignore