Don't use Bundler to run Jekyll

That causes GemNotFound errors on Netlify, starting a few days ago.
It looks like their Bundler isn't looking for dependencies in the very
folder WHERE IT INSTALLED THEM.

Until/unless Netlify fixes it, we'll just have to do builds this way.

netlify-build.sh

@@ -14,7 +14,7 @@ echo "Generating module command/config pages"
 python document_sopel_modules.py --sopel=_sopel
 
 echo "Building Jekyll site"
-bundler exec jekyll build
+jekyll build
 
 echo "Installing Sphinx"
 pip install sphinx