bump schema to v5.1, allows to cross-reference placeholders

data/fields/building/levels_building.json

@@ -3,7 +3,7 @@
     "type": "number",
     "minValue": 0,
     "label": "{building/levels}",
-    "placeholder": "2, 4, 6...",
+    "placeholder": "{building/levels}",
     "prerequisiteTag": {
         "key": "building",
         "valueNot": "no"

interim/source_strings.yaml

@@ -431,8 +431,6 @@ en:
         terms: '[translate with synonyms or related terms for ''Underground Levels'', separated by commas]'
       building/levels_building:
         # building:levels=*
-        # building/levels_building field placeholder
-        placeholder: 2, 4, 6...
       building/material:
         # building:material=*
         label: Material

package.json

@@ -20,7 +20,7 @@
     "translations": "node scripts/translations.js"
   },
   "devDependencies": {
-    "@ideditor/schema-builder": "~5.0.0",
+    "@ideditor/schema-builder": "~5.1.0",
     "prettier": "~2.7.1"
   }
 }