build_library: Whitelist the new Go 1.9 GLSA

This is the same case as the previous one.  Our Go 1.8 package has
the fix, but none of the older unsupported versions do.  Since we
have multiple installed versions and this says anything less than
Go 1.9 is vulnerable, we have to whitelist it until all older
versions of Go are removed from the OS.

build_library/test_image_content.sh

@@ -5,6 +5,7 @@
 GLSA_WHITELIST=(
 	201412-09 # incompatible CA certificate version numbers
 	201710-23 # we handle Go differently; drop when 1.9 builds everything
+	201803-03 # same as above, drop when all Go < 1.9 packages are gone
 )
 
 glsa_image() {