package.json: change version to v0.27.0-dev

Updates #1557

Change-Id: I72e573bae799fcce08bd4ff0119e25e524239316
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/329209
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

Author: hyangah

package-lock.json

@@ -1,7 +1,7 @@
 {
   "name": "go",
   "displayName": "Go",
-  "version": "0.26.0-dev",
+  "version": "0.27.0-dev",
   "preview": true,
   "publisher": "golang",
   "description": "Rich Go language support for Visual Studio Code",