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, 3 insertions, 3 deletions

diff --git a/activerecord/test/cases/migrator_test.rb b/activerecord/test/cases/migrator_test.rb
index 9809d83315..f05ca900aa 100644
--- a/activerecord/test/cases/migrator_test.rb
+++ b/activerecord/test/cases/migrator_test.rb
@@ -357,11 +357,11 @@ class MigratorTest < ActiveRecord::TestCase
   end
 
   private
-  def m(name, version, &block)
+  def m(name, version)
     x = Sensor.new name, version
     x.extend(Module.new {
-      define_method(:up) { block.call(:up, x); super() }
-      define_method(:down) { block.call(:down, x); super() }
+      define_method(:up) { yield(:up, x); super() }
+      define_method(:down) { yield(:down, x); super() }
     }) if block_given?
   end