Add missing import

Author: jmini

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElmClientCodegen.java

@@ -17,6 +17,7 @@
 
 package org.openapitools.codegen.languages;
 
+import io.swagger.v3.oas.models.OpenAPI;
 import io.swagger.v3.oas.models.media.ArraySchema;
 import io.swagger.v3.oas.models.media.NumberSchema;
 import io.swagger.v3.oas.models.media.Schema;