Improve INSTALL.sh script to include in STAMPED_VERSION the TAG date instead of date of latest commit

[mad-jrodriguez]

Currently, the INSTALL.sh script just get the date of the latest commit to generate the STAMPED_VERSION, however, multiple tags (tags with message, no light tags), that points to the same commit, will have the same STAMPED_VERSION.

With the proposed change, the STAMPED_VERSION will change if a new tag is created, even if the tag points to the same commit hash.