Error parsing Kubernetes minor version with extra characters (+)

[Douglas-Cleghorn]

Describe the bug

Some versions of Kubernetes return a plus sign (+) in the minor version number. When this happens Tye quits showing a misleading error message.

Drats! 'deploy' failed:
        Cannot apply manifests because kubectl is not installed

To Reproduce

1. Install Ubuntu 20.04 and MicroK8s
2. Configure kubectl using alias or by copying the config file
3. tye deploy -i

Further technical details

tye --version
0.6.0-alpha.21070.5+a42e4463943e3136dbd1de38474d8d62b802797c

Ubuntu 20.04.1

kubectl version -o json

{
  "clientVersion": {
    "major": "1",
    "minor": "20",
    "gitVersion": "v1.20.2",
    "gitCommit": "faecb196815e248d3ecfb03c680a4507229c2a56",
    "gitTreeState": "clean",
    "buildDate": "2021-01-13T13:28:09Z",
    "goVersion": "go1.15.5",
    "compiler": "gc",
    "platform": "linux/amd64"
  },
  "serverVersion": {
    "major": "1",
    "minor": "20+",
    "gitVersion": "v1.20.1-34+e7db93d188d0d1",
    "gitCommit": "e7db93d188d0d12f2fe5336d1b85cdb94cb909d3",
    "gitTreeState": "clean",
    "buildDate": "2021-01-11T23:50:46Z",
    "goVersion": "go1.15.6",
    "compiler": "gc",
    "platform": "linux/amd64"
  }
}

This line is the problem:

"minor": "20+",