Update r-introduction-2018-03-26.md
Update r-introduction-2018-03-26.md
sheffield-bioinformatics-core/sheffield-bioinformatics-core.github.io,sheffield-bioinformatics-core/sheffield-bioinformatics-core.github.io,sheffield-bioinformatics-core/sheffield-bioinformatics-core.github.io,sheffield-bioinformatics-core/sheffield-bioinformatics-core.github.io