Go < 1.9: Compatibility issue

[corona10]

We met some issues related to Go version.
For example, Go 1.9 moved to C99 float division.
As the result, we need to change unit test codes. (See #384)
However, this approach is not cool enough to support old Go version.
So, we need to update unit tests codes to support Go < 1.9 also Go 1.9

[sinramyeon]

I tried to use it Go 1.8 and 1.7 and some test were failed. Which go versions are compatible?

[corona10]

@hero0926 For test. Use 1.9 :)