Changed WebView package name in docs to com.google.android.webview.

Bug: none
Change-Id: Icac95a25ce49080d19b8c35fda6944c38bd4bf37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1685525
Auto-Submit: Chris Mumford <cmumford@google.com>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#674154}