added linter && precommit

Author: bpingris

backend/.eslintrc

@@ -0,0 +1,9 @@
+{
+    "parserOptions": {
+        "ecmaVersion": 6
+    },
+    "rules": {
+        "semi": ["error", "always"],
+        "quotes": ["error", "double"]
+    }
+}