don't brew update, hopefully fixes #2532

(cherry picked from commit 6049a07b74b55856d5be999bac4b4d49a5317d35)

.travis/install.sh

@@ -4,8 +4,6 @@ set -e
 set -x
 
 if [[ "$(uname -s)" == 'Darwin' ]]; then
-    brew update || brew update
-
     if [[ "${OPENSSL}" != "0.9.8" ]]; then
         brew outdated openssl || brew upgrade openssl
     fi