fileformats.json -> fileformats.jsonformat

By renaming the file, we make it possible to syntax check via running
"python jsonformat.py". "python json.py" gives a module ambiguity warning because
"impor json" is used in the file.

Author: rocky

mathics/builtin/fileformats/jsonformat.py

@@ -6,7 +6,7 @@
 
 from mathics.core.builtin import Builtin, String
 from mathics.core.evaluation import Evaluation
-from mathics.eval.fileformats.json import eval_JSONImport
+from mathics.eval.fileformats.jsonformat import eval_JSONImport
 
 
 class ImportJSON(Builtin):