Merge pull request #357 from lbryio/no-brew-error

Fix error on brew when package is already installed

packaging/travis/setup_osx.sh

@@ -7,5 +7,19 @@ wget https://www.python.org/ftp/python/2.7.11/python-2.7.11-macosx10.6.pkg
 sudo installer -pkg python-2.7.11-macosx10.6.pkg -target /
 pip install -U pip
 brew update
-brew install openssl
-brew link --force openssl
+
+# follow this pattern to avoid failing if its already
+# installed by brew:
+# http://stackoverflow.com/a/20802425
+if brew ls --versions gmp > /dev/null; then
+    echo 'gmp is already installed by brew'
+else
+    brew install gmp
+fi
+
+if brew ls --versions openssl > /dev/null; then
+    echo 'openssl is already installed by brew'
+else
+    brew install openssl
+    brew link --force openssl
+fi