Update .editorconfig with new properties. Close gh-915.

See http://editorconfig.org

.editorconfig

-; This file is for unifying the coding style for different editors and IDEs.
-; More information at http://EditorConfig.org
+# This file is for unifying the coding style for different editors and IDEs
+# editorconfig.org
 
 root = true
 
-; All JavaScript files should use tabs unless specified otherwise
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+# Tabs in JS unless otherwise specified
 [**.js]
 indent_style = tab