pkg(mono-6.12.0): update to match

packages/mono-6.12.0/build.sh

@@ -13,4 +13,7 @@ cd mono
 make -j$(nproc) 
 DESTDIR=build/tmp make install -j$(nproc)
 
-mv build/tmp/piston/packages/mono/6.12.0/mono-6.12.0 ../../output
+mv build/tmp/piston/packages/mono/6.12.0/mono-6.12.0 ../../mono-6.12.0
+
+cd ../../
+rm -rf build

packages/mono-6.12.0/environment

@@ -1 +1 @@
-export PATH=$PWD:$PATH
+export PATH=$PWD/mono-6.12.0:$PATH

packages/mono-6.12.0/metadata.json

@@ -2,6 +2,5 @@
     "language": "mono",
     "version": "6.12.0",
     "author": "Thomas Hobson <thomas@hexf.me>",
-    "dependencies": {},
     "aliases": ["csharp", "cs"]
 }