Read sonatype credentials from env (#64)

Read properties as default but if missing, try env.
Nice for local and CI.

Author: ferhatelmas

build.gradle

@@ -110,8 +110,8 @@ publishing {
         maven {
             url 'https://oss.sonatype.org/service/local/staging/deploy/maven2/'
             credentials {
-                username = sonatypeUsername
-                password = sonatypePassword
+                username = hasProperty('sonatypeUsername') ? sonatypeUsername : System.getenv('sonatypeUsername')
+                password = hasProperty('sonatypePassword') ? sonatypePassword : System.getenv('sonatypePassword')
             }
         }
     }