resolveHeaders: Ensure any header schema $ref is resolved

Author: kerrykimbrough

modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/ResolverFully.java

@@ -217,6 +217,13 @@ private void resolveHeaders(Map<String, Header> headers) {
                 Map<String,Example> resolved = resolveExample(examples);
                 resolvedValue.setExamples(resolved);
             }
+            Schema schema = resolvedValue.getSchema();
+            if(schema != null) {
+                Schema resolvedSchema = resolveSchema( schema);
+                if(resolvedSchema != null) {
+                    resolvedValue.setSchema( resolvedSchema);
+                }
+            }
             header.setValue(resolvedValue);
         }
     }