getrebar: use more portable chmod
getrebar: use more portable chmod

Mode 0700 makes Travis sad in our build environment, where the getrebar script
may be executed inside a build container and somehow that permission makes a
subsequent docker build command fail with `Error checking context:
'no permission to read from
'/home/travis/build/PagerDuty/event-rule-engine/deps/re2/support/rebar''.`.

I think that mode 0700 offers no security here and 0755 should prevent such
little issues.

tuncer/re2,tuncer/re2