Update dependency @sourcegraph/prettierrc to v3 (#81)

Author: renovate[bot]

package.json

@@ -139,7 +139,7 @@
     "last 1 Safari versions"
   ],
   "devDependencies": {
-    "@sourcegraph/prettierrc": "^2.2.0",
+    "@sourcegraph/prettierrc": "^3.0.0",
     "@sourcegraph/tsconfig": "^4.0.0",
     "@sourcegraph/tslint-config": "^12.3.1",
     "@types/mkdirp-promise": "5.0.0",

yarn.lock

@@ -709,10 +709,10 @@
     rxjs "^6.3.3"
     sourcegraph "^23.0.0"
 
-"@sourcegraph/prettierrc@^2.2.0":
-  version "2.2.0"
-  resolved "https://registry.yarnpkg.com/@sourcegraph/prettierrc/-/prettierrc-2.2.0.tgz#af4a6fcd465b0a39a07ffbd8f2d3414d01e603e8"
-  integrity sha512-kRdHxdAppxYnN7qAQjNTyuG05pjYHFtEUquZauXVXBeaGB4sye3uSkb8wgi34jeaUHG/gWp2f5hQgCCBMizjjA==
+"@sourcegraph/prettierrc@^3.0.0":
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/@sourcegraph/prettierrc/-/prettierrc-3.0.0.tgz#716b64b287565f98f539f76bea206912ab4d03b3"
+  integrity sha512-ziLujsC3IESHGYdtiJ7yVjte9i7mr6jKWTYtCVqgOWeY1Er0/xsQ/sdZIyK61tD282wvd7VjS4pk5RoGEN7biw==
 
 "@sourcegraph/tsconfig@^4.0.0":
   version "4.0.0"