Standard 201703L for fuerte

[andr1972]

Problem with fuerte can be solved changing

velocypack/CMakeLists.txt

Line 6 in d11b92e

set(CMAKE_CXX_STANDARD 11 CACHE STRING "target C++ standard")

from set(CMAKE_CXX_STANDARD 11 CACHE STRING "target C++ standard")
to set(CMAKE_CXX_STANDARD 17 CACHE STRING "target C++ standard")
see: arangodb/fuerte#27