[PR 128] CMake: Fix error locating GSL when building without Hunter

Error was:

| CMake Error at cmake/dependencies.cmake:22 (find_package):
|   By not providing "FindMicrosoft.GSL.cmake" in CMAKE_MODULE_PATH this
|   project has asked CMake to find a package configuration file provided by
|   "Microsoft.GSL", but CMake did not find one.
|
|   Could not find a package configuration file provided by "Microsoft.GSL"
|   with any of the following names:
|
|     Microsoft.GSLConfig.cmake
|     microsoft.gsl-config.cmake

Author: eigendude

cmake/dependencies.cmake

@@ -12,7 +12,6 @@ find_package(Boost CONFIG REQUIRED date_time filesystem random system)
 
 # https://docs.hunter.sh/en/latest/packages/pkg/Microsoft.GSL.html
 hunter_add_package(Microsoft.GSL)
-find_package(Microsoft.GSL CONFIG REQUIRED)
 
 # https://www.openssl.org/
 hunter_add_package(OpenSSL)