Specify encoding to avoid invalid multibyte errors

This will fix the "invalid multibyte char (US-ASCII)" error I got when running it in cygwin with Ruby 1.9

$ influxdb-cli
/usr/bin/influxdb-cli:23:in `load': /usr/lib/ruby/gems/1.9.1/gems/influxdb-cli-0.1.2/bin/influxdb-cli:30: invalid multibyte char (US-ASCII) (SyntaxError)
/usr/lib/ruby/gems/1.9.1/gems/influxdb-cli-0.1.2/bin/influxdb-cli:30: invalid multibyte char (US-ASCII)
/usr/lib/ruby/gems/1.9.1/gems/influxdb-cli-0.1.2/bin/influxdb-cli:30: syntax error, unexpected $end, expecting keyword_end
    puts '? ready'
            ^
        from /usr/bin/influxdb-cli:23:in `<main>'
Merge pull request #6 from jbripley/multibytefix

Specify encoding to avoid invalid multibyte errors