Merge branch 'hotfix/1.25.20'
do not print rvm is not a shell function warning in rvm do, update #2683, fix #2703
Update CONTRIBUTING.md

do not ask for `--trace`, update #2699
do not allow installing ree with ree - avoid endless loop, fix #2698
do not dispay 0 nanoseconds in installer debugging
backport Hash#reject regression fix for 2.1.0-railsexpress and 2.1.1-railsexpress
Merge pull request #2713 from skaes/hash-reject-regression-fix

backport Hash#reject regression fix for 2.1.0- and 2.1.1-railsexpress
Indented code blocks in help/tools.md

Markdown expects 4 spaces of indentation for code blocks.
Merge pull request #2716 from tobiashm/patch-1

Indented code blocks in help/tools.md
separate sed commands, update #2709
Merge branch 'master' of github.com:wayneeseguin/rvm
simplifying sed, update #2709
1.25.21
Merge branch 'master' into hotfix/1.25.21
Merge branch 'hotfix/1.25.21' into stable