Fix horizontal overflow for SampleCode component

[ericyliu]

fixes issue #687

• not the most elegant fix, but prevents the horizontal overflow. We could consider making the code in the box smaller incrementally with less horizontal screen space to prevent line wrapping, but that's not a perfect solution either
• also removes some extra padding at the bottom of SampleCode

[alexdavid]

Should we add a horizontal scrollbar to long codeblocks instead of wrapping? I think I've seen that more often than wrapping, but I don't feel strongly

[ericyliu]

that's a good point, it'll look nicer for the parts that are visible, let me change that