Fix casing for NuGet package ecosystem

Correct the casing of 'NuGet' to 'nuGet' in the configuration.

Author: vaclavhluzek

.github/dependabot.yml

@@ -5,7 +5,7 @@
 
 version: 2
 updates:
-  - package-ecosystem: "NuGet" # See documentation for possible values
+  - package-ecosystem: "nuGet" # See documentation for possible values
     directory: "/" # Location of package manifests
     schedule:
       interval: "weekly"