Don't use `_.template` for variable interpolation

It depends on `eval` which is unsafe.

CHANGES.md

 # Changelog
 
+## 3.3.4 (Unreleased)
+
+- Avoid `eval` (via `_.template` from lodash).
+
 ## 3.3.3 (2018-02-14)
 
 ### Bugfixes

src/converse-core.js

@@ -1862,7 +1862,7 @@
             i18n.fetchTranslations(
                 _converse.locale,
                 _converse.locales,
-                _.template(_converse.locales_url)({'locale': _converse.locale}))
+                u.interpolate(_converse.locales_url, {'locale': _converse.locale}))
             .catch(_.partial(_converse.log, _, Strophe.LogLevel.FATAL))
             .then(finishInitialization)
             .catch(_.partial(_converse.log, _, Strophe.LogLevel.FATAL));

src/utils.js

@@ -646,6 +646,14 @@
         return promise;
     };
 
+    u.interpolate = function (string, o) {
+        return string.replace(/{{{([^{}]*)}}}/g,
+            (a, b) => {
+                var r = o[b];
+                return typeof r === 'string' || typeof r === 'number' ? r : a;
+            });
+    };
+
     u.safeSave = function (model, attributes) {
         if (u.isPersistableModel(model)) {
             model.save(attributes);