Log Message:
Update devel/ruby-parslet to 1.6.0.

pkgsrc changes:

  - Add OVERRIDE_GEMSPEC for blankslate, it requires ~> 2.0 whereas we provide
    blankslate 3.1.3.  Testing with ruby-jekyll (the primary driver for this
    update) suggests it works ok.

upstream changes:

  + EXPERIMENTAL: Parslet accelerators permit replacing parts of your parser
    with optimized atoms using pattern matching. Look at
    examples/optimized_erb.rb or the introduction to the feature in
    qed/accelerators.md.

  + infix_expression permits to declare an infix expression parser (think
    calculator) directly. This will solve many of the problems we have
    more elegantly.

  + Rspec 3 syntax, though hideous, should now work.

  - Drops 1.8.7 compatibility.

  ! A performance anomaly when parsing multibyte characters has been detected
    and fixed with the help of Zach Moazeni (@zmoazeni).

  ! A few small bug fixes and optimisations have been introduced. API should
    remain unchanged.