cppzmq: Error buildng on Ubuntu 16.04

Of the two steps in the readme, the first (compile libzmq) worked ok. The second step fails:

cd cppzmq/build/
cmake ..

-- Detected CPPZMQ Version - 4.3.1
-- cppzmq v4.3.1
CMake Error at /usr/share/cmake-3.5/Modules/ExternalProject.cmake:1888 (message):
  Could not extract tarball filename from url:

    https://raw.githubusercontent.com/catchorg/Catch2/Catch1.x/single_include/catch.hpp
Call Stack (most recent call first):
  /usr/share/cmake-3.5/Modules/ExternalProject.cmake:2459 (_ep_add_download_command)
  tests/cmake/catch.cmake:3 (ExternalProject_Add)
  tests/CMakeLists.txt:12 (include)


-- Configuring incomplete, errors occurred!
See also "/home/simon/git_projects/cppzmq/build/CMakeFiles/CMakeOutput.log".