Log Message:
Update devel/rebar to 2.6.2.

- rebar/532: Automatically clean neotoma-generated erl files,
  regression test
- rebar/549: Add Windows continuous integration through AppVeyor
- rebar/551: fprof: document Cachegrind support
- rebar/556: fprof: further document Cachegrind support
- rebar/557: Fix windows eunit tests
- rebar/558: Add qualified name tests docs (see pr #119)
- rebar/560: Lock retest dependency
- rebar/562: Add support for Windows integration testing
- rebar/567: Allow windows release to use etc conf dir
- rebar/570: xref: fix dialyzer warning introduced in 69802f63120
- rebar/573: Provide additional debug logging on relup generation
- rebar/578: Add the latest OTP 18 version to the Travis build
- rebar/580: Additional Common Test regression tests
- rebar/581: Update retest dependency url
- rebar/586: Ensure ebin created for dia compiler
- rebar/587: rebar_require_vsn: Update regexp to account for newer
  OTP versions
- rebar/588: Look for ct .spec files in the ct_dir that was
  specified
- rebar/589: Introduce REBAR_DEPS_PREFER_LIBS env variable to
  alter search behaviour
- rebar/590: Treat port env vars as expandable only if they self
  reference
- rebar/591: Fix/eunit tests surefire crash
- rebar/594: Introduce REBAR_VSN_CACHE_FILE env variable to
  load/save vsn cache
- rebar/599: Fix bug when running gcc in cross_sizeof
- rebar/602: Support full-source rebar3-style deps (deps without
  Version Regexes)
- rebar/603: add deprecated message
- rebar/605: Add necessary OSX flags for port driver linking
- rebar/606: Revert 'Treat port env vars as expandable only if
  they self reference'