Fix typos in interrogate

dtool/src/interrogate/interrogate.cxx

@@ -550,7 +550,7 @@ main(int argc, char **argv) {
 
     output_include
       << "/*\n"
-      << " * This file generated by:\n"
+      << " * This file was generated by:\n"
       << " * " << command_line << "\n"
       << " *\n"
       << " */\n\n";
@@ -572,7 +572,7 @@ main(int argc, char **argv) {
 
     output_code
       << "/*\n"
-      << " * This file generated by:\n"
+      << " * This file was generated by:\n"
       << " * " << command_line << "\n"
       << " *\n"
       << " */\n\n";