Replace (slower) block.call with (faster) yield

Performance optimization: `yield` with an implicit `block` is faster than `block.call`.
See http://youtu.be/fGFM_UrSp70?t=10m35s and the following benchmark:

```ruby
require 'benchmark/ips'

def fast
 yield
end

def slow(&block)
 block.call
end

Benchmark.ips do |x|
 x.report('fast') { fast{} }
 x.report('slow') { slow{} }
end

# => fast    154095 i/100ms
# => slow     71454 i/100ms
# =>
# => fast  7511067.8 (±5.0%) i/s -   37445085 in   4.999660s
# => slow  1227576.9 (±6.8%) i/s -    6145044 in   5.028356s
```

1 files changed, 2 insertions, 2 deletions

diff --git a/activesupport/lib/active_support/testing/time_helpers.rb b/activesupport/lib/active_support/testing/time_helpers.rb
index 1112c6e0b1..8c63815660 100644
--- a/activesupport/lib/active_support/testing/time_helpers.rb
+++ b/activesupport/lib/active_support/testing/time_helpers.rb
@@ -90,7 +90,7 @@ module ActiveSupport
       #     Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00
       #   end
       #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
-      def travel_to(date_or_time, &block)
+      def travel_to(date_or_time)
         if date_or_time.is_a?(Date) && !date_or_time.is_a?(DateTime)
           now = date_or_time.midnight.to_time
         else
@@ -102,7 +102,7 @@ module ActiveSupport
 
         if block_given?
           begin
-            block.call
+            yield
           ensure
             travel_back
           end