Fix decompile script json regex

When Mojang added 1.13.2-pre2 to their manifest page it exposed a flaw
in the way the script's regex was getting the version json manifest.

I've tweaked the regex such that it will always first get the version
entry and then use that entry to get the json url, rather than trying to
do the whole thing in one shot.

Fixes GH-1582

scripts/decompile.sh

@@ -25,7 +25,11 @@ versionjson="$workdir/Minecraft/$minecraftversion/$minecraftversion.json"
 if [ ! -f "$versionjson" ]; then
     echo "Downloading $minecraftversion JSON Data"
     verescaped=$(echo ${minecraftversion} | sed 's/\./\\./g')
-    jsonurl=$(curl -s "https://launchermeta.mojang.com/mc/game/version_manifest.json" | grep -oE "https://.*?${verescaped}.json")
+    echo $verescaped
+    verentry=$(curl -s "https://launchermeta.mojang.com/mc/game/version_manifest.json" | grep -oE "{\"id\": \"${verescaped}\".*?\.json")
+    echo $verentry
+    jsonurl=$(echo $verentry | grep -oE https:\/\/.*?\.json)
+    echo $jsonurl
     curl -o "$versionjson" "$jsonurl"
     echo "$versionjson - $jsonurl"
 fi