Change test to address reviewer comments

Author: xwu

test/Interpreter/SDK/NSDecimal.swift

@@ -118,7 +118,7 @@ ten = Decimal(10)
 twenty.divide(by: ten)
 print(twenty) // CHECK: 2
 
-twenty = Decimal(20)
+twenty = NSDecimalNumber(mantissa: 2, exponent: 1, isNegative: false) as Decimal
 print(twenty.significand) // CHECK: 2
 print(twenty.exponent) // CHECK: 1
 print(twenty.ulp) // CHECK: 10