Fix Python warning about invalid escape sequences

Author: mkoncek

python/javapackages/maven/artifact.py

@@ -191,7 +191,7 @@ def interpolate(self, properties):
                getattr(self, member) and
                isinstance(getattr(self, member), str)):
                     curr_value = getattr(self, member)
-                    prog = re.compile("\\$\{([^}]+)\}")
+                    prog = re.compile(r"\${([^}]+)}")
                     props = prog.findall(curr_value)
                     for key in props:
                         try: