Fix catch2 download link

Fixes standardese#61.

Author: Zhansong Li

test/CMakeLists.txt

@@ -4,7 +4,7 @@
 
 # download catch
 if(NOT EXISTS ${CMAKE_CURRENT_BINARY_DIR}/catch.hpp)
-    file(DOWNLOAD https://raw.githubusercontent.com/philsquared/Catch/master/single_include/catch.hpp
+    file(DOWNLOAD https://raw.githubusercontent.com/catchorg/Catch2/master/single_include/catch2/catch.hpp
             ${CMAKE_CURRENT_BINARY_DIR}/catch.hpp)
 endif()