Update _csv.py

Doubling the stream read sample in detect() from 1024 to 2048 to make csv.Sniffer().sniff() more reliable.

src/tablib/formats/_csv.py

@@ -55,7 +55,7 @@ def import_set(cls, dset, in_stream, headers=True, skip_lines=0, **kwargs):
     def detect(cls, stream, delimiter=None):
         """Returns True if given stream is valid CSV."""
         try:
-            csv.Sniffer().sniff(stream.read(1024), delimiters=delimiter or cls.DEFAULT_DELIMITER)
+            csv.Sniffer().sniff(stream.read(2048), delimiters=delimiter or cls.DEFAULT_DELIMITER)
             return True
         except Exception:
             return False