Update 1.7.2-dev.json

Download fails because of missing backslash
The section
{
"name": "javax.persistence:persistence-api:1.0.2",
"url" : "http://repo.maven.apache.org/maven2"
}
for example gets translated to the url http://repo.maven.apache.org/maven2javax...
instead of http://repo.maven.apache.org/maven2/javax...
so there have to be a backslash at the end