grafana: build missing assets

Resolves void-linux/void-packages#205

srcpkgs/grafana/template

@@ -1,11 +1,12 @@
 # Template file for 'grafana'
 pkgname=grafana
 version=5.1.3
-revision=1
+revision=2
 build_style=go
 go_import_path=github.com/grafana/grafana
 go_package="${go_import_path}/pkg/cmd/grafana-cli ${go_import_path}/pkg/cmd/grafana-server"
 short_desc="The open platform for beautiful analytics and monitoring"
+hostmakedepends="nodejs-lts yarn"
 maintainer="Michael Aldridge <maldridge@VoidLinux.eu>"
 license="Apache-2.0"
 homepage="https://grafana.com"
@@ -17,14 +18,20 @@ _grafana_homedir="/var/lib/grafana"
 
 conf_files="/etc/grafana/grafana.ini"
 
+pre_build() {
+	yarn install --pure-lockfile
+}
+
+post_build() {
+	yarn run build
+}
+
 post_install() {
 	vlicense LICENSE.md
 
 	vmkdir var/lib/grafana
 	touch ${DESTDIR}/var/lib/grafana/.empty
 
-	# These artifacts are pulled from the binary distribution
-	# because they can't be built by Void.
 	vmkdir usr/share/grafana
 	vcopy public usr/share/grafana/
 	vcopy conf usr/share/grafana/