a small bug in Math.round with some values between 2**52 and 2**53

[Yaffle]

Math.round(2**53 - 1) should return 2**53 - 1

[MaxGraey]

Thanks! I created PR for this

[Yaffle]

@MaxGraey hi, I have tested other math functions against "JSMath" and found another small issue:
Math.acosh is not returning NaN for some values smaller than 1
Example:
Math.acosh(-9784.820766473835)

[MaxGraey]

@Yaffle Hmm, that's interesting. Basically AssemblyScript uses port of libm from musl for acosh. So pretty interesting how this handled by original libmusl. Math.acosh(-9784.820766473835) should definitely be a NaN

[MaxGraey]

btw some fix done for floating point version but not for double version