Upgrade react-scripts, switch from adm-zip to fflate.

adm-zip did not play nice with compiling to the browser after upgrading react-scripts

src/datasource/load_data.spec.ts

@@ -0,0 +1,23 @@
+import {loadFile} from './load_data';
+import {readFileSync} from 'fs';
+import {Blob} from 'buffer';
+
+describe('loadFile', () => {
+  global.URL.createObjectURL = jest.fn();
+
+  it('loads GEDCOM file', async () => {
+    const file = readFileSync('src/datasource/testdata/test.ged');
+    const blob = new Blob([file]);
+    const {gedcom, images} = await loadFile(blob);
+    expect(gedcom.length).toBe(4408);
+    expect(images).toEqual(new Map());
+  });
+
+  it('loads GEDZIP file', async () => {
+    const file = readFileSync('src/datasource/testdata/test.gdz');
+    const blob = new Blob([file]);
+    const {gedcom, images} = await loadFile(blob);
+    expect(gedcom.length).toBe(4408);
+    expect(images.size).toBe(1);
+  });
+});