Stablize random seed in shrink_sigma testing - #61

For 8 @example blocks, the 'text/html' representation of the resulting object is above the threshold (example_size_threshold: 8192 bytes). - 1 blocks had no image MIME show() method representation as an alternative. Sticking to the 'text/html' representation (largest block is 33930 bytes). On pages: getting_started.md - 7 blocks had 'image/svg+xml' fallback image representation available, using that. On pages: example_ordinal_data.md, getting_started.md