Fixed a character in the table (#2753)

I think the table stuff might just be a warning and not caught by the CI

Docs/source/io.rst

@@ -391,7 +391,7 @@ Derived variables
 | ``y_velocity``,                   | :math:`\ub = (\rho \ub)/\rho`                     |                             |                                         |
 | ``z_velocity``                    |                                                   |                             |                                         |
 +-----------------------------------+---------------------------------------------------+-----------------------------+-----------------------------------------+
-| ``enuc``                          | Nuclear energy generation rate / gram             | ``derenuc``                 | :math:`{\rm erg~g^{-1}~s^{-1}}`      |
+| ``enuc``                          | Nuclear energy generation rate / gram             | ``derenuc``                 | :math:`{\rm erg~g^{-1}~s^{-1}}`         |
 +-----------------------------------+---------------------------------------------------+-----------------------------+-----------------------------------------+
 
 problem-specific plotfile variables