install viewer dependencies before building

Tools/Gulp/package.json

@@ -62,11 +62,11 @@
         "webpack-stream": "^4.0.1"
     },
     "scripts": {
-        "install": "npm --prefix ../../Playground/ install ../../Playground/ && npm --prefix ../../tests/unit/ install ../../tests/unit/ && npm --prefix ../../Viewer/tests/ install ../../Viewer/tests/ && gulp deployLocalDev"
+        "install": "npm --prefix ../../Playground/ install ../../Playground/ && npm --prefix ../../tests/unit/ install ../../tests/unit/ && npm --prefix ../../Viewer/tests/ install ../../Viewer/tests/ && npm --prefix ../../Viewer/ install ../../Viewer/ && gulp deployLocalDev"
     },
     "dependencies": {
         "dts-bundle": "^0.7.3",
         "gulp-clean": "^0.4.0",
         "npm": "^5.8.0"
     }
-}
+}