message: chore(techdocs-common): bump default docker image
  A new release of `techdocs-container` has been published and as recommended [here](https://github.com/backstage/techdocs-container#release) the default container image used by the Techdocs Generator has been changed.
diff: @@ -42,7 +42,7 @@ export class TechdocsGenerator implements GeneratorBase {
  * The default docker image (and version) used to generate content. Public
  * and static so that techdocs-common consumers can use the same version.
  */
  - public static readonly defaultDockerImage = 'spotify/techdocs:v0.3.3';
  + public static readonly defaultDockerImage = 'spotify/techdocs:v0.3.4';
  private readonly logger: Logger;
  private readonly containerRunner: ContainerRunner;
  private readonly options: GeneratorConfig;
  