flutter: Fix kddockwidgets library name

So dart can load the correct one

src/flutter/dartagnan.json

@@ -1,3 +1,4 @@
 {
-    "createCMakeLists" : false
+    "createCMakeLists" : false,
+    "bindingsLibrary" : "kddockwidgets"
 }

src/flutter/generated/KDDockWidgets/dart/lib/Bindings.dart

@@ -47,7 +47,7 @@ class Library {
     // introduce our own env variable for the same use case
     var bindingsPath = Platform.environment["DARTAGNAN_BINDINGSLIB_PATH"] ?? "";
 
-    var libraryPath = bindingsLibraryName("KDDockWidgets");
+    var libraryPath = bindingsLibraryName("kddockwidgets");
     if (!bindingsPath.isEmpty) {
       libraryPath = bindingsPath + "/" + libraryPath;
     }