Update spring-cloud-config.adoc

fix typo
[#15] Installation of asciidoctor added to travis's before_install
Merge pull request #16 from achudzik/missingAsciiDoctorGem

[#15] Installation of asciidoctor added to travis's before_install
Merge pull request #11 from boostrack/patch-1

Update spring-cloud-config.adoc