Add json.hpp directly to the repository (for now)

Author: ingydotnet

src/cpp/.gitignore

@@ -4,14 +4,7 @@ ROOT := ../..
 #------------------------------------------------------------------------------
 default: help
 
-test: ext/nlohmann/json.hpp test-tap
-
-ext/nlohmann/json.hpp:
-	mkdir -p ext/nlohmann
-	curl -s https://raw.githubusercontent.com/nlohmann/json/develop/single_include/nlohmann/json.hpp > $@
-
-clean::
-	rm -fr ext/nlohmann/json.hpp
+test: test-tap
 
 #------------------------------------------------------------------------------
 include ../../.makefile/runtime.mk