FIX: change Max Ulp to 10 in almost-equal function.

Note: change to 10 according practice experience.
Some math function may produce different result on different arch.
For example.
  On x86 platform, exp 123 -> 2.6195173187490456e53
  On x86_64 platform, exp 123 -> 2.61951731874905e53
Merge pull request #944 from qtxie/max-ulps

FIX: change Max Ulp to 10 in almost-equal function.