Fix Dockerfile so that Quay.io can build Toil RNA-Seq image

[wshands]

Fix Dockerfile so that Quay.io can build Toil RNA-Seq image; this needs to be done because the Toil RNA-Seq pipeline cannot be registered properly on Dockstore so it can be used unless the image is built by Quay.io. At this time Toil RNA-Seq is built locally and the image is pushed to Quay.io. The Dockerfile was broken when the build of Toil RNA-Seq was synchronized with the build of the Docker images for different Docker versions, e.g. 1.12.3 etc.

[wshands]

Not necessary for Quay.io to build the image since it turns out Dockstore does not require Quay.io to build the image. Instead the images are pushed to Quay.io after being built locally, and then registered with Dockstore.