Fix typo in menu.lua documentation

[ghost]

A usage example in menu.lua has the following text:

When using rules.match_any instead of rules.match, a menu of clients with different classes could be build.

It should instead say:

When using rules.match_any instead of rules.match, a menu of clients with different classes could be built.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (375d9d7) 91.00% compared to head (bc2da1d) 91.01%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3876   +/-   ##
=======================================
  Coverage   91.00%   91.01%           
=======================================
  Files         901      901           
  Lines       57565    57566    +1     
=======================================
+ Hits        52389    52392    +3     
+ Misses       5176     5174    -2     

Flag	Coverage Δ
gcov	91.01% <ø> (+<0.01%)	⬆️
luacov	93.72% <ø> (-0.01%)	⬇️

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Files	Coverage Δ
lib/awful/menu.lua	57.48% <ø> (ø)

... and 3 files with indirect coverage changes