Fix braintree plugin doc typo

Author: reshmabidikar

userguide/tutorials/braintree-plugin.adoc

@@ -20,7 +20,7 @@ For example, to install the plugin via https://github.com/killbill/killbill-clou
 
 [source,bash]
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-kpm install_java_plugin braintree-plugin --destination=<path_to_install_plugin>
+kpm install_java_plugin braintree --destination=<path_to_install_plugin>
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 You can also install the plugin via the https://aviate.killbill.io/home[Aviate UI] "Plugin Marketplace" tab. Refer to the <<aviate_integration, Aviate Integration>> section below for more details.