add missing lib

lib/ArduinoJson/test/JsonObject/CMakeLists.txt

@@ -0,0 +1,20 @@
+# ArduinoJson - arduinojson.org
+# Copyright Benoit Blanchon 2014-2018
+# MIT License
+
+add_executable(JsonObjectTests 
+	basics.cpp
+	containsKey.cpp
+	get.cpp
+	invalid.cpp
+	iterator.cpp
+	prettyPrintTo.cpp
+	printTo.cpp
+	remove.cpp
+	set.cpp
+	size.cpp
+	subscript.cpp
+)
+
+target_link_libraries(JsonObjectTests catch)
+add_test(JsonObject JsonObjectTests)