Upgrade dependencies (#66)

Notable to end users. Upgrade of github.com/Masterminds/sprig to v3 containing a
lot of new template functions.

I have added the version number to the readme reference to sprig to make this
more clear. Before we linked to v3 docs but only supported v2 functions.

Another notable change is the new Go based auto completion framework in Go that
could replace some of our custom zsh completion logic.

README.md

@@ -189,7 +189,7 @@ $ shuttle has my.docker.image --stdout
 
 ### Template functions
 The `template` command along with commands taking a `--template` flag has multiple templating functions available.
-The [masterminds/sprig](http://masterminds.github.io/sprig) functions are available along with those described below.
+The [masterminds/sprig](http://masterminds.github.io/sprig) v3.2.2 functions are available along with those described below.
 
 Examples are based on the below `shuttle.yaml` file.
 

go.mod

@@ -3,22 +3,13 @@ module github.com/lunarway/shuttle
 go 1.15
 
 require (
-	github.com/Masterminds/semver v1.4.2 // indirect
-	github.com/Masterminds/sprig v2.16.0+incompatible
-	github.com/aokoli/goutils v1.0.1 // indirect
+	github.com/Masterminds/sprig/v3 v3.2.2
 	github.com/cli/safeexec v1.0.0
-	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-cmd/cmd v1.3.0
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
-	github.com/google/uuid v1.0.0 // indirect
-	github.com/huandu/xstrings v1.2.0 // indirect
-	github.com/imdario/mergo v0.3.6 // indirect
-	github.com/inconshreveable/mousetrap v1.0.0 // indirect
-	github.com/pkg/errors v0.8.1
-	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/spf13/cobra v0.0.4-0.20181127133106-d2d81d9a96e2
-	github.com/spf13/pflag v1.0.1 // indirect
-	github.com/stretchr/testify v1.2.2
-	golang.org/x/crypto v0.0.0-20180621125126-a49355c7e3f8 // indirect
-	gopkg.in/yaml.v2 v2.2.1
+	github.com/mitchellh/copystructure v1.1.1 // indirect
+	github.com/pkg/errors v0.9.1
+	github.com/spf13/cobra v1.1.3
+	github.com/stretchr/testify v1.7.0
+	gopkg.in/yaml.v2 v2.4.0
 )