Update base_classes/NXdetector_channel.nxdl.xml

Co-authored-by: soph-dec <73243774+soph-dec@users.noreply.github.com>

base_classes/NXdetector_channel.nxdl.xml

@@ -37,7 +37,7 @@
  will vary according to the situation) and the general ordering principle is slowest to fastest.
  The type of each dimension should follow the order of scan points, detector output (e.g. pixels),
  then time-of-flight (i.e. spectroscopy, spectrometry). Note that the output of a detector is not limited 
- to single values (0D), lists (1D) and images (2), but three or higher dimensional arrays can be produced 
+ to single values (0D), lists (1D) and images (2D), but three or higher dimensional arrays can be produced 
  by a detector at each trigger.
  </doc>