Update Cobra and pflag, and use built-in --version feature

[thaJeztah]

This updates cobra and pflag to tagged releases, and uses the new built-in --version feature.

Also hides [flags] in the usage output of commands, using the new .DisableFlagsInUseLine option, instead of the temporary workaround added in 8e600e1 (#642)

Before this change:

docker run
"docker run" requires at least 1 argument.
See 'docker run --help'.

Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...] [flags]

Run a command in a new container

After this change:

docker run
"docker run" requires at least 1 argument.
See 'docker run --help'.

Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Run a command in a new container

Bump spf13/cobra to v0.0.3

Use a tagged release of Cobra

spf13/cobra@34ceca5...v0.0.3

Relevant changes:

• Add CalledAs method to cobra.Command (w/ tests) spf13/cobra#567 Add CalledAs method to cobra.Command
• Update error message for missing required flags spf13/cobra#580 Update error message for missing required flags
• Add support for --version flag spf13/cobra#584 Add support for --version flag
• cmd: Fix #612 spf13/cobra#614 If user has a project in symlink, just use its destination folder and work there
• terminates the flags when -- is found in commandline spf13/cobra#649 terminates the flags when -- is found in commandline
• Add support for ignoring parse errors spf13/cobra#662 Add support for ignoring parse errors
• doc: hide hidden parent flags spf13/cobra#686 doc: hide hidden parent flags

Also various improvements were added for generating Bash
completion scripts (currently not used by us)

Bump spf13/pflag to v1.0.1

Use a tagged release of this package

spf13/pflag@97afa5e...v1.0.1

Relevant changes:

• DurationSlice: implementation and tests spf13/pflag#122 DurationSlice: implementation and tests
• Implement BytesHex type of argument spf13/pflag#115 Implement BytesHex type of argument
• Add uintSlice and boolSlice to name prettifier spf13/pflag#150 Add uintSlice and boolSlice to name prettifier
• Add multiline wrapping support spf13/pflag#155 Add multiline wrapping support
• doc: clarify difference between string slice vs. array spf13/pflag#158 doc: clarify difference between string slice vs. array
• add ability to ignore unknown flags spf13/pflag#160 add ability to ignore unknown flags
• Allow Users To Show Deprecated Flags spf13/pflag#163 Allow Users To Show Deprecated Flags

[thaJeztah]

Wasn't sure if we needed this; without this, docker will be printed lowercase (i.e., name of the binary). If we think that's ok, I can remove this

[thaJeztah]

Unfortunately still needed; our flag-description has a short-hand (-v), and looks like;

 -v, --version            Print version information and quit

Whereas the built-in flag for Cobra doesn't have a shorthand, and looks like this;

      --version            version for docker

[vieux]

LGTM