(helm): update Cobra to version 0.0.4

The version of Cobra used in dev-v3 is older than the one used
for the master branch (helm v2). Although the dev-v3 branch
was based on master and therefore had the same Cobra version
originally, it was changed a couple of times to choose Cobra
tagged versions instead.

However, the currently used 0.0.3 version of Cobra is older than
the version of Cobra used on the master branch. Therefore, some of the
improvements made to Cobra and used by helm v2 are not available
to helm v3 currently.

This commit brings Cobra to its latest available version of 0.0.4.

Bringing Cobra up-to-date is essential for upcoming work being
prepared for dynamic bash-completion; there are bug fixes in
Cobra that are necessary for dynamic bash-completion to work
properly. Specifically,
    spf13/cobra#730
 which fixes
    spf13/cobra#694
is essential to avoid the risk of colliding and possibly
breaking kubectl dynamic bash-completion once helm v3 has its
own dynamic completion.

Signed-off-by: Marc Khouzam <marc.khouzam@ville.montreal.qc.ca>

Gopkg.toml

@@ -109,3 +109,7 @@
 [[constraint]]
   name = "github.com/xeipuuv/gojsonschema"
   version = "1.1.0"
+
+[[constraint]]
+  name = "github.com/spf13/cobra"
+  version = "0.0.4"