Updated minimum coverage percentages

refs https://github.com/TryGhost/Toolbox/issues/475

- Increased statements and lines minimum required numbers as we have increased out baseline and should keep the bar as hight as possible

ghost/core/.c8rc.json

@@ -6,10 +6,10 @@
     "text-summary",
     "cobertura"
   ],
-  "statements": 57,
+  "statements": 61,
   "branches": 80,
   "functions": 51,
-  "lines": 57,
+  "lines": 61,
   "include": [
     "core/{*.js,frontend,server,shared}"
   ],