Don't bind blocks if not necessary

Having this benchmark:


    require 'lotus/view'
    require 'benchmark/ips'

    module Lotus
      module View
        module Rendering
          class NullTemplate
            def fast_render(scope, locals = {})
              yield
            end
          end
        end
      end
    end


    template = Lotus::View::Rendering::NullTemplate.new

    Benchmark.ips do |x|
      x.report("blk.call") do
        template.render nil do
        end
      end
      x.report("yield") do
        template.fast_render nil do
        end
      end
    end

yields such results:

    Calculating -------------------------------------
                blk.call     87147 i/100ms
                   yield    155453 i/100ms
    -------------------------------------------------
                blk.call  1516789.7 (±6.6%) i/s -    7581789 in   5.019669s
                   yield  5565781.8 (±1.2%) i/s -   27826087 in   5.000213s

Therefore I replaced unneeded blk.call with yield. I found no documentation, which would need an update.