Fix Shellcheck SC2166: test -a is not well defined

Prefer [ p ] && [ q ] as [ p -a q ] is not well defined.

https://github.com/koalaman/shellcheck/wiki/SC2166

Signed-off-by: Dan Callahan <danc@element.io>

scripts-dev/check-newsfragment

@@ -45,7 +45,7 @@ matched=0
 for f in `git diff --name-only FETCH_HEAD... -- changelog.d`; do
     # check that any modified newsfiles on this branch end with a full stop.
     lastchar=`tr -d '\n' < $f | tail -c 1`
-    if [ $lastchar != '.' -a $lastchar != '!' ]; then
+    if [ $lastchar != '.' ] && [ $lastchar != '!' ]; then
         echo -e "\e[31mERROR: newsfragment $f does not end with a '.' or '!'\e[39m" >&2
         echo -e "$CONTRIBUTING_GUIDE_TEXT" >&2
         exit 1