telegraf: fix source-build upgrade, remove postinstall

Author: cho-m

Formula/t/telegraf.rb

@@ -25,10 +25,9 @@ class Telegraf < Formula
   def install
     ldflags = "-s -w -X github.com/influxdata/telegraf/internal.Version=#{version}"
     system "go", "build", *std_go_args(ldflags:), "./cmd/telegraf"
-    (etc/"telegraf.conf").write Utils.safe_popen_read(bin/"telegraf", "config")
-  end
 
-  def post_install
+    (buildpath/"telegraf.conf").write Utils.safe_popen_read(bin/"telegraf", "config")
+    etc.install "telegraf.conf"
     # Create directory for additional user configurations
     (etc/"telegraf.d").mkpath
   end
@@ -44,7 +43,6 @@ def post_install
   test do
     assert_match version.to_s, shell_output("#{bin}/telegraf --version")
     (testpath/"config.toml").write shell_output("#{bin}/telegraf -sample-config")
-    system bin/"telegraf", "-config", testpath/"config.toml", "-test",
-           "-input-filter", "cpu:mem"
+    system bin/"telegraf", "-config", testpath/"config.toml", "-test", "-input-filter", "cpu:mem"
   end
 end