Fix formatting in highlight docs
Fix formatting in highlight docs

Right now, the `\1` in the plain text gets escaped to just "1" in the rendered docs.  Wrap it in `tt` tags to keep the \ there as intended.

[ci skip]

kmcphillips/rails,esparta/rails,BlakeWilliams/rails,Stellenticket/rails,yahonda/rails,Vasfed/rails,kddeisz/rails,MSP-Greg/rails,Edouard-chin/rails,yahonda/rails,georgeclaghorn/rails,Stellenticket/rails,BlakeWilliams/rails,Envek/rails,esparta/rails,Stellenticket/rails,joonyou/rails,kmcphillips/rails,MSP-Greg/rails,kddeisz/rails,esparta/rails,joonyou/rails,georgeclaghorn/rails,georgeclaghorn/rails,yawboakye/rails,yahonda/rails,rails/rails,yawboakye/rails,bogdanvlviv/rails,esparta/rails,Erol/rails,EmmaB/rails-1,yawboakye/rails,rails/rails,BlakeWilliams/rails,Erol/rails,lcreid/rails,Edouard-chin/rails,betesh/rails,BlakeWilliams/rails,MSP-Greg/rails,Vasfed/rails,Stellenticket/rails,EmmaB/rails-1,Envek/rails,rails/rails,kmcphillips/rails,joonyou/rails,rails/rails,bogdanvlviv/rails,Envek/rails,bogdanvlviv/rails,lcreid/rails,betesh/rails,Erol/rails,Edouard-chin/rails,yawboakye/rails,kddeisz/rails,joonyou/rails,betesh/rails,georgeclaghorn/rails,yahonda/rails,Erol/rails,EmmaB/rails-1,bogdanvlviv/rails,betesh/rails,kmcphillips/rails,Envek/rails,MSP-Greg/rails,lcreid/rails,kddeisz/rails,lcreid/rails,Vasfed/rails,Edouard-chin/rails,Vasfed/rails