Fix setup script: extras_require, not extra_require (#808)

Author: robsdedude

setup.py

@@ -34,7 +34,7 @@
 install_requires = [
     "pytz",
 ]
-extra_require = {
+extras_require = {
     "pandas": ["pandas>=1.0.0"],
 }
 classifiers = [
@@ -70,7 +70,7 @@
     "keywords": "neo4j graph database",
     "url": "https://github.com/neo4j/neo4j-python-driver",
     "install_requires": install_requires,
-    "extra_require": extra_require,
+    "extras_require": extras_require,
     "classifiers": classifiers,
     "packages": packages,
     "entry_points": entry_points,