Vagrant: Do not create database if it already exists

Patch by @oldskool.
Closes #24.

scripts/environment.sh

@@ -63,7 +63,7 @@ cp /vagrant/scripts/aliases ~/.aliases
 ### Create rc file ###
 echo "source ~/.aliases" >> ~/.bashrc
 
-mysql -u root -proot -e 'create database flarum'
+mysql -u root -proot -e 'create database if not exists flarum'
 
 ### Setup flarum/core and install dependencies ###
 cd /vagrant/flarum/core