swap es-dsl dep to es6-dsl

Author: felliott

setup.py

@@ -60,7 +60,7 @@ def read(fname):
         "metrics",
         "statistics",
     ),
-    install_requires=["elasticsearch-dsl>=6.3.0,<7.0.0"],
+    install_requires=["elasticsearch6-dsl>=6.3.0,<7.0.0"],
     extras_require=EXTRAS_REQUIRE,
     classifiers=[
         "Operating System :: OS Independent",