Update dependency nyc to v15

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
nyc	devDependencies	major	14.1.1 -> 15.0.0

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Release Notes

istanbuljs/nyc

v15.0.0

Compare Source

⚠ BREAKING CHANGES

• The flow and jsx parser plugins are no longer
  enabled by default.
• Node.js 8 is now required to run nyc
• Remove NYC_ROOT_ID and NYC_INSTRUMENTER environmental
  variables.
• The root field has been removed from processinfo
  files.

Features

• Add --use-spawn-wrap=true option (#​1169) (df4de4d)
• Add .cjs, .mjs, .ts, .tsx, .jsx to default extensions (#​1110) (914b776), closes #​1103
• Allow nyc instrument to instrument code in place (#​1149) (7783284)
• Drop node.js 6, upgrade dependencies (#​1134) (00c3b34)
• Filenames relative to project cwd in coverage reports (#​1212) (5258e9f)
• Use @​istanbuljs/schema for yargs setup (#​1194) (fd40d49)
• Use istanbul-lib-processinfo (#​1145) (7943413)
• Use source base name to prefix cache files (#​1144) (5c1b7a9)

Bug Fixes

• Avoid source-map module during signal-exit handler (#​1191) (83eb629)
• Better error handling for main execution, reporting (#​1229) (dfd629d)
• Correct handling of source-maps for pre-instrumented files (#​1216) (8411a26), closes #​1208
• Drop coverage produced by nyc --all for files that were tested (#​1155) (fc1bbbf), closes #​1113 #​1124 #​1148
• Honor eager setting (false by default) (#​1179) (c18fb0a)
• Remove vestigial environment variables (#​1078) (cfd3da0)

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