typo: chmod +x instead of -x for post-checkout script (#2006)

Author: masinter

scripts/install-repo-checks.sh

@@ -7,7 +7,7 @@
 
 rm -f .git/hooks/post-checkout
 cp scripts/post-checkout .git/hooks/post-checkout &&
-    chmod -x .git/hooks/post-checkout &&
+    chmod +x .git/hooks/post-checkout &&
     echo copy made: &&
     ls -l .git/hooks/post-checkout &&
     exit 0