Fix typo in routing.rst

[markgras]

This fixes a small typo in the routing docs. I did not think that this warranted an issue, nor a changelog entry. If you disagree, please let me know and I can make those additional changes.

[codecov]

Codecov Report

Merging #1984 (3833744) into master (ac1331e) will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1984      +/-   ##
==========================================
+ Coverage   92.68%   92.78%   +0.09%     
==========================================
  Files          29       29              
  Lines        3241     3241              
  Branches      566      566              
==========================================
+ Hits         3004     3007       +3     
+ Misses        160      158       -2     
+ Partials       77       76       -1     

Impacted Files	Coverage Δ
sanic/server.py	81.61% <0.00%> (+0.56%)	⬆️

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