gotipplay: fix GOTIP environment variable to be string
gotipplay: fix GOTIP environment variable to be string

Change-Id: If2aca632dd49cc161e7034d7231937b53e18c592
Reviewed-on: https://go-review.googlesource.com/c/playground/+/366179
Trust: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Reviewed-by: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/playground,golang/playground,golang/playground