Fix SQLAlchemy 1.2.0 compatibility (#411)

Author: Gr1N

Diff for: aiopg/sa/result.py

@@ -100,7 +100,6 @@ def __init__(self, result_proxy, metadata):
         self._keymap = keymap = {}
         self.keys = []
         dialect = result_proxy.dialect
-        typemap = dialect.dbapi_type_map
         assert dialect.case_sensitive, \
             "Doesn't support case insensitive database connection"
 
@@ -121,9 +120,7 @@ def __init__(self, result_proxy, metadata):
             name, obj, type_ = (
                 colname,
                 None,
-                result_map.get(
-                    colname,
-                    typemap.get(coltype, sqltypes.NULLTYPE))
+                result_map.get(colname, sqltypes.NULLTYPE),
             )
 
             processor = type_._cached_result_processor(dialect, coltype)

Diff for: requirements.txt

@@ -11,5 +11,5 @@ pytest-cov==2.5.1
 pytest-sugar==0.9.0
 pytest-timeout==1.2.1
 sphinxcontrib-asyncio==0.2.0
-sqlalchemy==1.1.15
+sqlalchemy==1.2.0
 psycopg2==2.6.2