Fix escape error

lib/util.js

@@ -9,11 +9,14 @@ const parse = v => {
   } catch (e) {}
 }
 
-const escapeHtml = s =>
-  s
-    .replace(/</g, '&lt;')
-    .replace(/>/g, '&gt;')
-    .replace(/\//g, '&#x2F;')
+const escapeHtml = s => {
+  if (typeof s === 'string') {
+    return s
+      .replace(/</g, '&lt;')
+      .replace(/>/g, '&gt;')
+      .replace(/\//g, '&#x2F;')
+  }
+}
 
 export const parseRGBA = obj => `rgba(${obj.r},${obj.g},${obj.b},${obj.a})`