Fixup mkCfg

Previously, dollar signs in the tf2 config str would be interpreted as bash variables during build

tf2/packages/default.nix

@@ -14,15 +14,14 @@ let
       inherit hash name;
     };
 
-  mkCfg = name: body:
-    pkgs.runCommand name {} ''
-      ${lib.toShellVar "name" name}
-      mkdir -p $out/cfg "$(dirname "$out/cfg/$name")"
-      tee "$out/cfg/$name.cfg" << SUPER_UNIQUE_EOF
-      // Generated by tf2.nix
-
-      ${body}
-      SUPER_UNIQUE_EOF
+  mkCfg = path: body:
+    pkgs.runCommand path {} ''
+      ${lib.toShellVar "pathPart" path}
+      path="$out/cfg/$pathPart.cfg"
+      mkdir -p "$(dirname -- "$path")"
+      echo "// Generated by tf2.nix" >> "$path"
+      echo >> "$path"
+      echo ${lib.escapeShellArg body} >> "$path"
     '';
 
   mergeTf2Configs = configs: