Implement yarn completion (Bash-it#2190)

* feat (completion): add yarn completion

Author: tbhaxor

clean_files.txt

@@ -76,6 +76,7 @@ completion/available/system.completion.bash
 completion/available/vault.completion.bash
 completion/available/vuejs.completion.bash
 completion/available/wpscan.completion.bash
+completion/available/yarn.completion.bash
 
 # libraries
 lib/appearance.bash

completion/available/yarn.completion.bash

@@ -0,0 +1,5 @@
+# shellcheck shell=bash
+about-completion "yarn cli completions"
+
+# shellcheck disable=SC1090 source=../../vendor/github.com/dsifford/yarn-completion/yarn
+source "${BASH_IT}/vendor/github.com/dsifford/yarn-completion/yarn"