我在 angular 6 项目中使用 ng2-pdf-viewer，
在项目编译时，它会出现以下错误
node_modules/@types/pdfjs-dist/index.d.ts(63,39) 中的错误：错误 TS2304：找不到名称“未知”。
node_modules/@types/pdfjs-dist/index.d.ts(65,34)：错误 TS2304：找不到名称“未知”。
node_modules/@types/pdfjs-dist/index.d.ts(80,31)：错误 TS2304：找不到名称“未知”。
node_modules/@types/pdfjs-dist/index.d.ts(82,30): 错误 TS2304: 找不到名称“未知”
我的 package.json 文件如下面的帖子
"dependencies": {
"@angular/animations": "^6.1.10",
"@angular/common": "^6.1.0",
"@angular/compiler": "^6.1.0",
"@angular/core": "^6.1.0",
"@angular/forms": "^6.1.0",
"@angular/http": "^6.1.0",
"@angular/platform-browser": "^6.1.0",
"@angular/platform-browser-dynamic": "^6.1.0",
"@angular/router": "^6.1.0",
"@ngx-translate/core": "^11.0.1",
"@ngx-translate/http-loader": "^4.0.0",
"@vimeo/player": "^2.10.0",
"@types/node": "10.3.1",
"angular-6-datatable": "~0.8.0",
"angular-6-social-login": "~1.1.1",
"bootstrap": "^4.3.1",
"core-js": "^2.5.4",
"crypto-js": "~3.1.9-1",
"devextreme": "^19.1.5",
"devextreme-angular": "^19.1.5",
"font-awesome": "~4.7.0",
"jquery": "^3.4.1",
"ng2-drag-drop": "^3.0.2",
"ng2-pdf-viewer": "^6.0.2",
"ng5-slider": "^1.2.4",
"ngx-bootstrap": "^3.3.0",
"ngx-drag-scroll": "~7.4.2",
"ngx-image-cropper": "~1.3.10",
"ngx-loading": "^3.0.1", …