$ gwtc ./guava.wiki
Unhandled rejection Error: Unknown language: "buildr"
Please report this to https://github.com/markedjs/marked.
at Object.highlight (/usr/lib/node_modules/github-wikito-converter/node_modules/highlight.js/lib/highlight.js:506:13)
at Renderer.mainRenderer.code (/usr/lib/node_modules/github-wikito-converter/dist/markdown.js:34:79)
at Parser.tok (/usr/lib/node_modules/github-wikito-converter/node_modules/marked/lib/marked.js:1058:28)
at Parser.parse (/usr/lib/node_modules/github-wikito-converter/node_modules/marked/lib/marked.js:1003:17)
at Function.Parser.parse (/usr/lib/node_modules/github-wikito-converter/node_modules/marked/lib/marked.js:985:17)
at marked (/usr/lib/node_modules/github-wikito-converter/node_modules/marked/lib/marked.js:1322:19)
at Markdown.convertMarkdownString (/usr/lib/node_modules/github-wikito-converter/dist/markdown.js:109:14)
at Markdown.convertMarkdownFile (/usr/lib/node_modules/github-wikito-converter/dist/markdown.js:116:19)
at WikiConverter.<anonymous> (/usr/lib/node_modules/github-wikito-converter/dist/wiki-converter.js:87:41)
at Array.forEach (<anonymous>)
at WikiConverter.computePages (/usr/lib/node_modules/github-wikito-converter/dist/wiki-converter.js:83:27)
at WikiConverter.getPages (/usr/lib/node_modules/github-wikito-converter/dist/wiki-converter.js:96:14)
at HtmlWriter.write (/usr/lib/node_modules/github-wikito-converter/dist/html-writer.js:33:34)
at WikiConverter.<anonymous> (/usr/lib/node_modules/github-wikito-converter/dist/wiki-converter.js:60:43)
at tryCatcher (/usr/lib/node_modules/github-wikito-converter/node_modules/bluebird/js/main/util.js:26:23)
at Promise._settlePromiseFromHandler (/usr/lib/node_modules/github-wikito-converter/node_modules/bluebird/js/main/promise.js:510:31)
Looks like it's because of code snippets which highlight.js does not recognize. The wiki mentioned above has buildr and proguard as code language. Replacing them with shell worked for me.
Unable to convert Google Guava wiki at https://github.com/google/guava/wiki