Integer operation should result in Integer.

Should raise `RangeError` if the operation overflows.

test/t/integer.rb

@@ -125,10 +125,6 @@ assert('Integer#<<', '15.2.8.3.12') do
   assert_equal 23, 46 << -1
 
   skip unless Object.const_defined?(:Float)
-
-  # Overflow to Integer
-  assert_float 9223372036854775808.0, 1 << 63
-  assert_float(-13835058055282163712.0, -3 << 62)
 end
 
 assert('Integer#>>', '15.2.8.3.13') do