Fix Help details.

Details of help start with lowercase.
Before:
<pre>
    -g, --gemfile GEMFILE            Gemfile path
    -G, --gem-path GEM_INSTALL_PATH  Gemfile install path
        --use-shared-gems            Enable gems not installed into gem-path

        --version                    Show version
</pre>

After:
<pre>
    -g, --gemfile GEMFILE            gemfile path
    -G, --gem-path GEM_INSTALL_PATH  gemfile install path
        --use-shared-gems            enable gems not installed into gem-path

        --version                    show version
</pre>