Dependabot: versioning-strategy increase-if-necessary (#340)

PubGrub is a library, so we should widen the range where possible to not force users to upgrade versions.

Author: konstin

.github/dependabot.yml

@@ -12,5 +12,6 @@ updates:
 
   - package-ecosystem: "cargo"
     directory: "/"
+    versioning-strategy: "increase-if-necessary"
     schedule:
       interval: "monthly"