Add instruction to run all tests in CONTRIBUTING (#1150)
Add instruction to run all tests in CONTRIBUTING (#1150)

This instruction existed before the last update to the document.
thoughtbot/shoulda-matchers,biow0lf/shoulda-matchers,thoughtbot/shoulda-matchers,biow0lf/shoulda-matchers,biow0lf/shoulda-matchers,reacuna/shoulda-matchers,biow0lf/shoulda-matchers,guialbuk/shoulda-matchers,reacuna/shoulda-matchers,guialbuk/shoulda-matchers,guialbuk/shoulda-matchers,reacuna/shoulda-matchers,thoughtbot/shoulda-matchers,reacuna/shoulda-matchers,guialbuk/shoulda-matchers,thoughtbot/shoulda-matchers