chore: bump typescript version to 3.8

It's been supported in the latest versions of @typescript-eslint packages
typescript-eslint/typescript-eslint#1696

Author: haoqunjiang

package.json

@@ -84,7 +84,7 @@
     "request-promise-native": "^1.0.8",
     "rimraf": "^3.0.2",
     "semver": "^6.1.0",
-    "typescript": "~3.7.5",
+    "typescript": "~3.8.3",
     "vuepress": "^1.3.0",
     "webpack": "^4.0.0",
     "yorkie": "^2.0.0"

packages/@vue/cli-plugin-typescript/package.json

@@ -42,7 +42,7 @@
     "@types/chai": "^4.2.11",
     "@types/jest": "^24.0.19",
     "@types/mocha": "^5.2.6",
-    "typescript": "~3.7.5",
+    "typescript": "~3.8.3",
     "vue-class-component": "^7.2.3",
     "vue-property-decorator": "^8.4.1"
   }

packages/@vue/cli-ui/package.json

@@ -60,7 +60,7 @@
     "prismjs": "^1.19.0",
     "rss-parser": "^3.7.6",
     "shortid": "^2.2.15",
-    "typescript": "~3.7.5",
+    "typescript": "~3.8.3",
     "vue-cli-plugin-apollo": "^0.21.3",
     "watch": "^1.0.2"
   },