Remove dependency package jszip (#189)

Jszip package is used to export files to zip format, but it is based on GPL protocol, so remove it.
diff --git a/front-end/package.json b/front-end/package.json
index 3408ff6..8a2ca34 100644
--- a/front-end/package.json
+++ b/front-end/package.json
@@ -44,7 +44,6 @@
     "font-awesome": "4.7.0",
     "js-cookie": "2.2.0",
     "jsonlint": "1.6.3",
-    "jszip": "3.1.5",
     "mockjs": "1.0.1-beta3",
     "normalize.css": "7.0.0",
     "nprogress": "0.2.0",
diff --git a/front-end/src/vendor/Export2Zip.js b/front-end/src/vendor/Export2Zip.js
deleted file mode 100644
index 1c442ef..0000000
--- a/front-end/src/vendor/Export2Zip.js
+++ /dev/null
@@ -1,37 +0,0 @@
-/*
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-/* eslint-disable */
-require('script-loader!file-saver');
-import JSZip from 'jszip'
-
-export function export_txt_to_zip(th, jsonData, txtName, zipName) {
-  const zip = new JSZip()
-  const txt_name = txtName || 'file'
-  const zip_name = zipName || 'file'
-  const data = jsonData
-  let txtData = `${th}\r\n`
-  data.forEach((row) => {
-    let tempStr = ''
-    tempStr = row.toString()
-    txtData += `${tempStr}\r\n`
-  })
-  zip.file(`${txt_name}.txt`, txtData)
-  zip.generateAsync({
-    type: "blob"
-  }).then((blob) => {
-    saveAs(blob, `${zip_name}.zip`)
-  }, (err) => {
-    alert('导出失败')
-  })
-}