Delete vendored code and update CI to Go 1.13 (#158)

As the Go community transitions to using the modules ecosystem,
we want to only support one way of managing dependencies.
So this change moves to only using Go modules for dependency management.

This means that our effective minimum Go version increases to Go 1.11.
To account for this, we also update:
  - the documentation
  - Makefile
  - CI scripts

1 files changed, 0 insertions, 44 deletions

diff --git a/vendor/github.com/urfave/cli/category.go b/vendor/github.com/urfave/cli/category.go
deleted file mode 100644
index 1a60550..0000000
--- a/vendor/github.com/urfave/cli/category.go
+++ /dev/null
@@ -1,44 +0,0 @@
-package cli
-
-// CommandCategories is a slice of *CommandCategory.
-type CommandCategories []*CommandCategory
-
-// CommandCategory is a category containing commands.
-type CommandCategory struct {
-	Name     string
-	Commands Commands
-}
-
-func (c CommandCategories) Less(i, j int) bool {
-	return c[i].Name < c[j].Name
-}
-
-func (c CommandCategories) Len() int {
-	return len(c)
-}
-
-func (c CommandCategories) Swap(i, j int) {
-	c[i], c[j] = c[j], c[i]
-}
-
-// AddCommand adds a command to a category.
-func (c CommandCategories) AddCommand(category string, command Command) CommandCategories {
-	for _, commandCategory := range c {
-		if commandCategory.Name == category {
-			commandCategory.Commands = append(commandCategory.Commands, command)
-			return c
-		}
-	}
-	return append(c, &CommandCategory{Name: category, Commands: []Command{command}})
-}
-
-// VisibleCommands returns a slice of the Commands with Hidden=false
-func (c *CommandCategory) VisibleCommands() []Command {
-	ret := []Command{}
-	for _, command := range c.Commands {
-		if !command.Hidden {
-			ret = append(ret, command)
-		}
-	}
-	return ret
-}