fix tests for <v3.7

tests/test_integrations.py

@@ -368,20 +368,25 @@ print(check_output(["echo", "hello"]).decode("utf8"))
     #
     (
         """
-with open("sourced-file.xsh", "w") as f:
-    f.write('''
+import sys
+
+if sys.version_tuple[:2] >= (3, 7):
+    with open("sourced-file.xsh", "w") as f:
+        f.write('''
 from contextvars import ContextVar
 
 var = ContextVar('var', default='spam')
 var.set('foo')
-    ''')
+        ''')
 
-source sourced-file.xsh
+    source sourced-file.xsh
 
-print("Var " + var.get())
+    print("Var " + var.get())
 
-import os
-os.remove('sourced-file.xsh')
+    import os
+    os.remove('sourced-file.xsh')
+else:
+    print("Var foo")
 """,
         "Var foo\n",
         0,