allow for another version of zero intercept models

Author: atrigila

assets/schema_contrasts.json

@@ -15,7 +15,7 @@
                     },
                     "formula": {
                         "type": "string",
-                        "pattern": "^~\\s*[a-zA-Z0-9_]*(\\s*([:+*])\\s*[a-zA-Z0-9_]*)*$"
+                        "pattern": "^~\\s*(?:[A-Za-z0-9_]+(?:\\s*(?:[:+*])\\s*[A-Za-z0-9_]+)*)?(?:\\s*-\\s*1)?$"
                     },
                     "comparison": {
                         "type": "array",