RFR: Ignore IntelliJ files and Maven target directory

[Henri Tremblay]

Ignore IntelliJ files and Maven target directory

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Commit messages:
 - Ignore IntelliJ files and Maven target directory

Changes: https://git.openjdk.java.net/jmh/pull/23/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmh&pr=23&range=00
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmh/pull/23.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh pull/23/head:pull/23

PR: https://git.openjdk.java.net/jmh/pull/23