Restrict active merchant to 1.48.x
Restrict active merchant to 1.48.x

https://github.com/solidusio/solidus/commit/adde7d7d33e3a7d860887eafcc6d96420fca8d36

Loosened the dependency on active merchant, which caused active merchant
to be bumped to 1.58 for solidus versions 1.3 or greater.

Unfortunately, 1.58 is not interface compatable with 1.48. This brings
back that restriction for people who opt to use solidus gateway until an
upgrade path is determined.

solidusio/solidus_gateway,solidusio/solidus_gateway