Bump to v4.0.0.

internal/toFunction.js

@@ -0,0 +1,15 @@
+define(['../identity'], function(identity) {
+
+  /**
+   * Converts `value` to a function if it's not one.
+   *
+   * @private
+   * @param {*} value The value to process.
+   * @returns {Function} Returns the function.
+   */
+  function toFunction(value) {
+    return typeof value == 'function' ? value : identity;
+  }
+
+  return toFunction;
+});