add 'try...catch' statement snippet to js-mode (#227)

* add 'try...catch' statement snippet to js-mode

For details, see below link:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch

* change variable name from `e` to `err` for Error object

snippets/js-mode/try-catch

@@ -0,0 +1,11 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: try...catch statement
+# key: try
+# --
+try {
+  $1
+} catch (err) {
+  $2
+}${3: finally {
+  $4
+}}