.vscodeignore: ignore more files in packaging

Change-Id: I5e7eff80dcfb90bcbda722bc31e0c43305e76f91
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/238897
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
diff --git a/.vscodeignore b/.vscodeignore
index 5de5988..529c5c2 100644
--- a/.vscodeignore
+++ b/.vscodeignore
@@ -12,3 +12,7 @@
 docs/
 *.md.nightly
 .github/**/*
+.prettierrc.json
+out/test/**
+.vscode-test/**
+SECURITY.md