[DOC] fix sym.arange doc (apache#14237)

* fix doc

* Update symbol.py

* Retrigger CI

python/mxnet/symbol/symbol.py

@@ -2912,6 +2912,7 @@ def hypot(left, right):
     else:
         raise TypeError('types (%s, %s) not supported' % (str(type(left)), str(type(right))))
 
+
 def eye(N, M=0, k=0, dtype=None, **kwargs):
     """Returns a new symbol of 2-D shpae, filled with ones on the diagonal and zeros elsewhere.
 
@@ -3002,11 +3003,16 @@ def full(shape, val, dtype=None, **kwargs):
 def arange(start, stop=None, step=1.0, repeat=1, infer_range=False, name=None, dtype=None):
     """Returns evenly spaced values within a given interval.
 
+    Values are generated within the half-open interval [`start`, `stop`). In other
+    words, the interval includes `start` but excludes `stop`. The function is
+    similar to the built-in Python function `range` and to `numpy.arange`,
+    but returns a `Symbol`.
+
     Parameters
     ----------
-    start : number
+    start : number, optional
         Start of interval. The interval includes this value. The default start value is 0.
-    stop : number, optional
+    stop : number
         End of interval. The interval does not include this value.
     step : number, optional
         Spacing between values.