Set shellcheck servity to warning+

Added the -S warning option to the shellcheck call to make informational
and style suggestions not throw errors in travis.  These types of things
can be picked up in code review.

Signed-off-by: Eric F Crist <ecrist@secure-computing.net>

.travis.yml

@@ -9,7 +9,7 @@ env:
 script:
  - which shellcheck
  - shellcheck -V
- - bash -c 'export SHELLCHECK_OPTS="-e SC2006"; shopt -s globstar; shellcheck **/*.sh easyrsa3/easyrsa'
+ - bash -c 'export SHELLCHECK_OPTS="-S warning -e SC2006"; shopt -s globstar; shellcheck **/*.sh easyrsa3/easyrsa'
  - bash -c 'pwd'
  - bash -c 'ls -la'
  - which openssl