diff --git a/.travis.yml b/.travis.yml
index dac8d278..2dc12586 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,7 @@
 language: node_js
 sudo: false
 node_js:
+  - "4"
   - "6"
   - "8"
   - "10"
diff --git a/postinstall.js b/postinstall.js
index a1202e0f..7737f220 100755
--- a/postinstall.js
+++ b/postinstall.js
@@ -1,5 +1,7 @@
 #!/usr/bin/env node
 
+'use strict';
+
 function isTrue(value) {
   return !!value && value !== '0' && value !== 'false';
 }