travis: require check when not explicitly disabled

.travis/build-pkgs

@@ -79,7 +79,7 @@ for repo in $(changed_repos "$commit_range"); do
 		fold_start "$pkgname" "Building package $qname"
 		cd $qname
 
-		if abuild -r; then
+		if REQUIRE_CHECK=1 abuild -r; then
 			checkapk || :
 			successful_pkgs="$successful_pkgs $qname"
 		else