chore(deps): Bump cross-spawn, gatsby, gatsby-plugin-manifest, gatsby-plugin-offline, gatsby-plugin-react-helmet, gatsby-plugin-sass, gatsby-plugin-sharp, gatsby-source-filesystem, gatsby-transformer-sharp and npm

chore(deps): Bump cross-spawn, gatsby, gatsby-plugin-manifest, gatsby-plugin-offline, gatsby-plugin-react-helmet, gatsby-plugin-sass, gatsby-plugin-sharp, gatsby-source-filesystem, gatsby-transformer-sharp and npm #20