write line separator to output properly formatted jsonlines

dev/archery/archery/cli.py

@@ -352,9 +352,12 @@ def benchmark_diff(ctx, src, preserve, suite_filter, benchmark_filter,
 
         regressions = 0
         runner_comp = RunnerComparator(runner_cont, runner_base, threshold)
+
+        # TODO(kszucs): test that the output is properly formatted jsonlines
         for comparator in runner_comp.comparisons:
             regressions += comparator.regression
             json.dump(comparator, output, cls=JsonEncoder)
+            output.write('\n')
 
         sys.exit(regressions)