x11-wm/hs-xmonad: Update 0.18.0 => 0.18.1

• Add WWW for source code repository.
• Mark as PIE_UNSAFE.
• Refer to ${MASTERDIR}/files as ${FILESDIR} instead of ${PATCHDIR} for semantical clarity.

Approved by: haskell@ (alven@)
Approved by: db@, yuri@ (Mentors, implicit)