fixed typo in gatsby-remark-prismjs README.md (#6165)
fixed typo in gatsby-remark-prismjs README.md (#6165)


ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,fk/gatsby,gatsbyjs/gatsby,0x80/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,0x80/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,fk/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,fk/gatsby