[release-branch.go1.15-security] go1.15.7

Change-Id: Ieec3576afa00cadf91166bf4df39037702635b86
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/957920
Reviewed-by: Roland Shoemaker <bracewell@google.com>

VERSION

diff --git a/VERSION b/VERSION
index ea3b51f..4b2ef0e 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-go1.15.6
\ No newline at end of file
+go1.15.7
\ No newline at end of file