Fixed missing packages.json file

PKGBUILD

@@ -20,6 +20,8 @@ prepare() {
     # patching
     cd "$srcdir/${pkgname%-git}"
     patch --strip=2 < ../../nimlangserver.patch # work around "Error: cannot open file: /usr/compiler/pathutils" https://github.com/nim-lang/langserver/issues/22
+    # download packages.json file
+    nimble refresh
 }
 
 pkgver() {
@@ -28,7 +30,6 @@ pkgver() {
 }
 
 build() {
-    # FIXME missing "packages.json" file
     # change into source
     cd "$srcdir/${pkgname%-git}"
     # compile program