Fix typos in branding guidelines

[slel]

The branding guidelines available in the file brand_guide.pdf at

• https://github.com/jupyter/design/tree/main/brandguide

could be slightly improved:

• page 10, logo misuses:
  typo: obsured -> obscured
• page 11, condensed logo:
  vertical space above and below "jupyter" wordmark inside
  condensed logo should be labeled 1/15 H instead of H

See also: #38 #47 #54 #68 #69.