Don't use destructive operation on a frozen string
Don't use destructive operation on a frozen string

It seems that a string passed to `Lcoveralls::call' in
color_formatter.rb is frozen in ruby implementation(ruby-2.4). The
implementation is installed to travis-ci.

As the result, `capitalize!', a destructive operation on the string
causes errors like:

    Finished .info-file creation

    /home/.../lcoveralls/color_formatter.rb:46:in `capitalize!': can't
    modify frozen String (RuntimeError)

This change replaces `capitalize!' with `capitalize' to avoid the
error.

Signed-off-by: Masatake YAMATO <bdfff7006d3a5967c7c741d652a74f5445442e11@redhat.com>

pcolby/lcoveralls