previous release link spelling mistake

[paperplane]

Expected Behavior

(Previous versions will be available at previous/$VERSION_NUMBER, e.g. https://storage.googleapis.com/tekton-releases/pipeline/previous/v0.2.0/release.yaml.)

Actual Behavior

(Previous versions will be available at previous/$VERSION_NUMBER, e.g. https://storage.googleapis.com/tekton-releases/pipeline/previous/0.2.0/release.yaml.)

Steps to Reproduce the Problem

1. https://github.com/tektoncd/pipeline/blob/master/docs/install.md documentation
2. $VERSION_NUMBER is the format v0.2.0 not 0.2.0. download will fail

Additional Info