**Description of the change**

The kubeseal install command instructions for linux contained both wget
and curl commands. This change just uses curl.

**Benefits**

Reduce the dependencies need to run a one bash block install of
kubeseal.

**Possible drawbacks**

The user has wget installed but not curl, now both commands (version
get, and tar download) will fail.

**Additional information**

I ran into an issue where I copy and pasted the linux install commands
for kubeseal that contained the curl and jq to automatically pull the
version number, but I didn't have wget installed.

Signed-off-by: Dan Fredell <Dan.Fredell@gmail.com>