Update version number in snapcraft.yaml.

Author: daute

snap/snapcraft.yaml

@@ -1,7 +1,7 @@
 name: wxmaxima
-version: 21.04.0
+version: 21.05.0
 summary: A nightly build of wxMaxima, a gui for Maxima, a full-featured CAS.
-description: wxMaxima is a quite full-featured graphical user interface for maxima.
+description: wxMaxima is a quite full-featured graphical user interface for Maxima.
 confinement: strict
 grade: stable
 icon: data/io.github.wxmaxima_developers.wxMaxima.svg