Fixed correct string representation of schema write

Author: RagnarW

neo4j/v1/session.py

@@ -41,7 +41,7 @@ class which can be used to obtain `Driver` instances that are used for
 STATEMENT_TYPE_READ_ONLY = "r"
 STATEMENT_TYPE_READ_WRITE = "rw"
 STATEMENT_TYPE_WRITE_ONLY = "w"
-STATEMENT_TYPE_SCHEMA_WRITE = "sw"
+STATEMENT_TYPE_SCHEMA_WRITE = "s"
 
 
 class GraphDatabase(object):