fix(schema): do not recurse endlessly when writing cyclic schemas

the schema writer will now load the original schema file from disk, so that only minimal changes
will get made

fixes #185 for good

.gitignore

@@ -30,4 +30,5 @@ npm-debug.log
 # instanbul code coverage…
 coverage
 /examples/tmp-docs
-.nyc_output
+.nyc_output
+test/fixtures/cyclic-out/

lib/writeSchema.js

@@ -27,7 +27,7 @@ function writeSchema({ schemadir, origindir }) {
       const dirname = path.dirname(filename);
 
 
-      const out = Object.assign({}, schema);
+      const out = fs.readJSONSync(schema[s.filename]);
       if (schema[s.meta] && schema[s.meta].description) {
         // copy description from external file
         out.description = schema[s.meta].description;