Improve assert snippet

Author: Shougo

neosnippets/java.snip

@@ -29,7 +29,7 @@ snippet const_string
     static public final String ${1:var} = "${2}";${4}
 
 snippet assert
-    assert ${1:#:test} ${2:#:Failure message};${3}
+    assert ${1:#:test} : ${2:#:Failure message};${3}
 
 snippet if
     if (${1}) {