I am using some locally installed gems in my environment and I would like to change the `EXECUTABLE DIRECTORY` path to `~/.gem/bin`

How could I achieve this?

```
$gem env

  - RUBYGEMS VERSION: 2.2.2
  - RUBY VERSION: 2.1.5 (2014-11-13 patchlevel 273) [x86_64-linux]
  - INSTALLATION DIRECTORY: /home/flyer/.gem/ruby
  - RUBY EXECUTABLE: /usr/bin/ruby
  - EXECUTABLE DIRECTORY: /home/flyer/bin
  - SPEC CACHE DIRECTORY: /home/flyer/.gem/specs
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /home/flyer/.gem/ruby
     - /usr/share/gems
     - /usr/local/share/gems
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     - /usr/local/bin
     - /usr/local/sbin
     - /usr/bin
     - /usr/sbin
     - /bin
     - /sbin
     - /home/flyer/.local/bin
     - /home/flyer/bin
     - /home/flyer/.local/bin
     - /home/flyer/bin

```