PEP 387: Fix broken TIOBE link

[dr-carlos]

• Change is either:
  • To a Draft PEP
  • To an Accepted or Final PEP, with Steering Council approval
  • To fix an editorial issue (markup, typo, link, header, etc)
• PR title prefixed with PEP number (e.g. PEP 123: Summary of changes)

Link to TIOBE programming community index in PEP 387: Backwards Compatability Policy, was dead.
Updated with the new link.

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