plugin gets confused when upstream has any tags not intended as semver

[rozcietrzewiacz]

Examples:

index.docker.io/istio/proxy_init                  ...  46.0.0-f6aa463844d3fab60e5db283258370c4fcc72e19
index.docker.io/istio/galley                      ...  999450.0.0-fd4add69e26ba04d001b811863cba8175b22
index.docker.io/istio/mixer                       ...  7708199.0.0
(... and much more from istio ...)
registry.opensource.zalan.do/teapot/external-dns  ...  8170947.0.0
index.docker.io/improbable/thanos                 ...  2018.0.0-03-08-bartek-reloader-test1
index.docker.io/jaegertracing/all-in-one          ...  89133199.0.0

[strigona-worksight]

Some other examples:

quay.io/jetstack/cert-manager-cainjector               v0.13.1            7875368.0.0       23
docker.elastic.co/eck/eck-operator                     1.0.1              43.0.0            1
gcr.io/stackdriver-agents/metadata-agent-go            1.0.5              42086.0.0-bb2-5c2b-4c0f-958e-6c941fad073b4

[marccampbell]

This is difficult to handle. These parse as semver strings, but clearly not intended.

Would an acceptable solution here be to simply look for massive differences in semver? Projects don't often jump from 0.13.1 to 7875368.0.0, so we can safely ignore that outlier...

[marccampbell]

Put a PR up to handle this. I'm not sure if it will cause other problems though. This PR (#20) works by looking for Major version gaps in the semver list and ignoring anything after that gap.