Update ImageMagick package name on FreeBSD

Summary:
FreeBSD packages repository now provides
two versions of ImageMagick, 6 and 7.

"ImageMagick" is appended by the version number.

Test Plan: Install on WindRiver

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2123