Merge pull request scrapy#1951 from redapple/backport-1.1-pr1950

[backport][1.1] Place brackets on own lines with JsonItemExporter (PR scrapy#1950)

Author: redapple

scrapy/exporters.py

@@ -100,10 +100,10 @@ def __init__(self, file, **kwargs):
         self.first_item = True
 
     def start_exporting(self):
-        self.file.write(b"[")
+        self.file.write(b"[\n")
 
     def finish_exporting(self):
-        self.file.write(b"]")
+        self.file.write(b"\n]")
 
     def export_item(self, item):
         if self.first_item: