fix the JSONFormatter flush & close_section:right now flush will not …

…output n,and close_section will output n when m_stack has no entry.

src/common/Formatter.cc

@@ -240,7 +240,7 @@ void JSONFormatter::close_section()
   }
   m_ss << (entry.is_array ? ']' : '}');
   m_stack.pop_back();
-  if (!m_stack.size())
+  if (m_pretty && (!m_stack.size()))
     m_ss << "\n";
 }