Fix markdown for table (#650)

Author: MichaelMonashev

docs/encoders.rst

@@ -333,9 +333,14 @@ Mix Visual Transformer
 | Encoder   | Weights  | Params, M  |
 +===========+==========+============+
 | mit\_b0   | imagenet | 3M         |
++-----------+----------+------------+
 | mit\_b1   | imagenet | 13M        |
++-----------+----------+------------+
 | mit\_b2   | imagenet | 24M        |
++-----------+----------+------------+
 | mit\_b3   | imagenet | 44M        |
++-----------+----------+------------+
 | mit\_b4   | imagenet | 60M        |
++-----------+----------+------------+
 | mit\_b5   | imagenet | 81M        |
 +-----------+----------+------------+