Modifies Apache vhost definition to use single quotes
Modifies Apache vhost definition to use single quotes

Per #395, usage of double-quotes attempts to expand the string
`${APACHE_LOG_DIR}` within the vhost definition. Since that value may or
may not be set, and, if set, may not be correct for the vagrant image,
single quotes must be used to prevent expansion.

Tested and verified.

webimpress/ZendSkeletonApplication,webimpress/ZendSkeletonApplication,vrkansagara/ZendSkeletonApplication,vrkansagara/ZendSkeletonApplication