Update conftest.py

Improve security and efficiency of import statements.

Author: david-thrower

tests/conftest.py

@@ -1,8 +1,8 @@
 # Ensure the repository root is on sys.path so `import cerebros` works when
 # running tests without installing the package.
-import os
-import sys
+from os.path import abspath
+from sys import path
 
-ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), ".."))
-if ROOT not in sys.path:
-    sys.path.insert(0, ROOT)
+ROOT = abspath(os.path.join(os.path.dirname(__file__), ".."))
+if ROOT not in path:
+    path.insert(0, ROOT)