Update Golang compiler in fabric-baseimage for the z Systems platform to 1.7.5

The Golang compiler used by the z Systems platform needs to be upgraded from 1.7.3 to 1.7.5 to take advantage of Eliptic Curve digital signature acceleration. The improvements take advantage of the z Systems' "Single Instruction Multiple Data" (SIMD) capability to accelerate the Eliptic Curve digital signature acceleration.