meson: adjust nlohmann-json dependency

Simplify the nlohmann-json dependency in the meson.build and align
the wrap file name for consistency with the meson wrapdb.

Change-Id: I17dbb6eb1e26a8f9413a1d02c1233b88aa7d90bd
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/subprojects/nlohmann_json.wrap b/subprojects/nlohmann_json.wrap
new file mode 100644
index 0000000..3745380
--- /dev/null
+++ b/subprojects/nlohmann_json.wrap
@@ -0,0 +1,6 @@
+[wrap-git]
+revision = HEAD
+url = https://github.com/nlohmann/json.git
+
+[provide]
+nlohmann_json = nlohmann_json_dep