fix: deprecated syntax of lower substr (#3013)

* fixed import error syntax

* replace lower.substr with lower.substring

* remove redundant parameter

* fixed import syntax error

* fixed import syntax error

platform/core/src/extensions/ExtensionManager.js

@@ -365,5 +365,5 @@ export default class ExtensionManager {
  * @param {string} lower
  */
 function _capitalizeFirstCharacter(lower) {
-  return lower.charAt(0).toUpperCase() + lower.substr(1);
+  return lower.charAt(0).toUpperCase() + lower.substring(1);
 }