fix of coverity-push

tools/travis/travis_push_coverity.sh

@@ -7,7 +7,7 @@
 
 git fetch origin coverity_scan
 COMMITS=`git log --oneline --since=today.midnight | wc -l`
-if [[ "$COMMITS" -le "1" ]]; then
+if [ "$COMMITS" -le 1 ]; then
     #first commit a day - push changes to branch coverity_scan
     git clone -b coverity_scan https://$GITAUTH@github.com/acplt/open62541
     cd open62541