Typo fixup

Author: jbrockmendel

pandas/tests/frame/test_analytics.py

@@ -739,7 +739,7 @@ def var(x):
             return np.var(x, ddof=1)
 
         def std(x):
-            return x: np.std(x, ddof=1)
+            return np.std(x, ddof=1)
 
         def sem(x):
             return np.std(x, ddof=1) / np.sqrt(len(x))