package.json: activate extension onDebugInitialConfigurations

The extension should be activated before provideDebugConfigurations
method is called.

Updates golang/vscode-go#131

Change-Id: I06a3cf18da63c9bdae01d7ce8d177dfa872e4f21
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/267899
Trust: Suzy Mueller <suzmue@golang.org>
Run-TryBot: Suzy Mueller <suzmue@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/package.json b/package.json
index e7a4994..8160f84 100644
--- a/package.json
+++ b/package.json
@@ -95,6 +95,7 @@
     "onCommand:go.tools.install",
     "onCommand:go.locate.tools",
     "onCommand:go.show.commands",
+    "onDebugInitialConfigurations",
     "onDebugResolve:go"
   ],
   "main": "./dist/goMain.js",