Add connection: close HTTP header to mitigate connections errors

Author: vtourraine

SZNZotero/SZNZoteroAPIClient.m

@@ -66,6 +66,7 @@ - (id)initWithKey:(NSString *)key
         self.URLScheme = URLScheme;
         self.parameterEncoding = AFJSONParameterEncoding;
         [self setDefaultHeader:@"Zotero-API-Version" value:@"2"];
+        [self setDefaultHeader:@"Connection" value:@"close"];
     }
 
     return self;