style(3p/nix): Reformat project in Google C++ style

Reformatted with:

    fd . -e hh -e cc | xargs clang-format -i

third_party/nix/src/libexpr/json-to-value.hh

@@ -1,13 +1,12 @@
 #pragma once
 
-#include "eval.hh"
-
 #include <string>
+#include "eval.hh"
 
 namespace nix {
 
 MakeError(JSONParseError, EvalError)
 
-void parseJSON(EvalState & state, const string & s, Value & v);
+    void parseJSON(EvalState& state, const string& s, Value& v);
 
 }