fix: actualize the filter builder literal mock

Author: r0b1n

packages/shared/widget-plugin-test-utils/__mocks__/mendix/filters/builders.js

@@ -7,7 +7,7 @@ exports.literal = x => ({
         }
         switch (value.constructor.name) {
             case "String":
-                return "String";
+                return "string";
             case "Number":
             case "Big":
                 return "Numeric";

packages/shared/widget-plugin-test-utils/__tests__/filters/builders.test.ts

@@ -17,8 +17,8 @@ describe("mendix/filters/builders mock", () => {
     test.each([
         [true, "boolean"],
         [false, "boolean"],
-        ["!", "String"],
-        ["", "String"],
+        ["!", "string"],
+        ["", "string"],
         [new Big(0), "Numeric"],
         [new Big(0.49), "Numeric"],
         [new Big(-1), "Numeric"],