Allow jdk_version to be a string or number

Previously, the case statements checking the jdk_version failed
because they were assuming jdk_version was a string. For users overriding
this value and setting it to be a number, the case statement would never
match. This commit ensures we are always using a string when comparing
jdk_version.
Merge pull request #133 from socrata-cookbooks/fix_jdk_version_string

Allow jdk_version to be a string or number