sparkle: offer update only for supported os

Set minimum macOS version for sparkle updater to 10.14. The same
minimum version is required by qt 6. So only users with macOS 10.14
or higher will be offered to update jami to qt version on macOS.

Change-Id: I58b081a2a042db118d06724f7a6e9359feefb59c

sparkle/sparkle-xml-updater.sh

@@ -36,7 +36,7 @@ cat << EOFILE > ${REPO_FOLDER}/${SPARKLE_FILE}
             <pubDate>$DATE_RFC2822</pubDate>
             <sparkle:version>${BUILD}</sparkle:version>
             <sparkle:shortVersionString>${VERSION}</sparkle:shortVersionString>
-            <sparkle:minimumSystemVersion>10.13</sparkle:minimumSystemVersion>
+            <sparkle:minimumSystemVersion>10.14.0</sparkle:minimumSystemVersion>
             <enclosure url="${REPO_URL}/$(basename ${PACKAGE})" length="$PACKAGE_SIZE" type="application/octet-stream" sparkle:dsaSignature="$(./sign_update.sh ${PACKAGE} ${DSA_KEY})" />
         </item>
 $(echo -e "${ITEMS}")