Use yarn to install dependencies if yarn.lock is available (#32)

* Add check for yarn.lock and use yarn to install if available

* Add check for yarn executable

* Bump version

* Fix init script, add postinstall

* Fix shellcheck issues

* Tweak postinstall script

* Tweak postinstall script

* Remove postinstall

bin/motley-eslint-init.sh

@@ -1,2 +1,14 @@
-PKG=eslint-config-airbnb;
-npm info "$PKG@latest" peerDependencies --json | command sed 's/[\{\},]//g ; s/: /@/g' | xargs npm install --save-dev "$PKG@latest"
+#!/bin/bash
+
+PKG=eslint-config-airbnb
+
+# Default to installing using npm
+INSTALL="npm install --save-dev"
+
+# Is this a yarn project and yarn is found in PATH, then install using yarn
+if [[ -f $(PWD)/yarn.lock && -x $(which yarn) ]]
+then
+  INSTALL="yarn add --dev"
+fi
+
+npm info "$PKG@latest" peerDependencies --json | command sed 's/[\{\},]//g ; s/: /@/g' | xargs $INSTALL "$PKG@latest"

package.json

@@ -1,6 +1,6 @@
 {
   "name": "eslint-config-motley",
-  "version": "6.0.1",
+  "version": "6.1.0",
   "description": "Motley Agency's ESLint configuration",
   "main": ".eslintrc.js",
   "scripts": {