text: Title: ypeError: No matching definition for argument type(s) array(float64, 2d, C), array(int32, 1d, C), array(bool, 1d, C)
  Body: I am trying to reproduce example from readme. I get error in this line 
  ```
  # Generate signals
  fast_ma, slow_ma = vbt.MA.from_combinations(price, windows, 2)
  ```
  The error message is:
  ```
  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  <ipython-input-15-9abe364754ce> in <module>
        1 # Generate signals
  ----> 2 fast_ma, slow_ma = vbt.MA.from_combinations(price, windows, 2)
  
  C:\ProgramData\Anaconda3\lib\site-packages\vectorbt\indicators\indicators.py in from_combinations(cls, ts, windows, r, ewm, names, **kwargs)
      202             names = ['ma' + str(i+1) for i in range(r)]
      203         windows, ewm = reshape_fns.broadcast(windows, ewm, writeable=True)
  --> 204         cache_dict = cls.from_params(ts, windows, ewm=ewm, return_cache=True, **kwargs)
      205         param_lists = zip(*itertools.combinations(zip(windows, ewm), r))
      206         mas = []
  
  C:\ProgramData\Anaconda3\lib\site-packages\vectorbt\indicators\indicators.py in from_params(cls, ts, window, ewm, **kwargs)
       98             ```
       99         """
  --> 100         return super().from_params(ts, window, ewm, **kwargs)
      101 
      102     @classmethod
  
  C:\ProgramData\Anaconda3\lib\site-packages\vectorbt\indicators\factory.py in from_params(cls, name, return_raw, *args, **kwargs)
      614             results = from_params_pipeline(
      615                 ts_list, param_list, level_names, len(output_names),
  --> 616                 custom_func, *new_args, pass_lists=pass_lists, return_raw=return_raw, **kwargs)
      617             if return_raw or kwargs.get('return_cache', False):
      618                 return results
  
  C:\ProgramData\Anaconda3\lib\site-packages\vectorbt\indicators\factory.py in from_params_pipeline(ts_list, param_list, level_names, num_outputs, custom_func, pass_lists, param_product, broadcast_kwargs, return_raw, *args, **kwargs)
      405     # Perform main calculation
      406     if pass_lists:
  --> 407         output_list = custom_func(ts_list, param_list, *args, **kwargs)
      408     else:
      409         output_list = custom_func(*ts_list, *param_list, *args, **kwargs)
  
  C:\ProgramData\Anaconda3\lib\site-packages\vectorbt\indicators\factory.py in custom_func(ts_list, param_list, return_cache, cache, *args)
      778                 # Caching
      779                 if cache is None and caching_func is not None:
  --> 780                     cache = caching_func(*typed_ts_list, *param_list, *args)
      781                 if return_cache:
      782                     return cache
  
  ~\AppData\Roaming\Python\Python37\site-packages\numba\dispatcher.py in _explain_matching_error(self, *args, **kws)
      572         msg = ("No matching definition for argument type(s) %s"
      573                % ', '.join(map(str, args)))
  --> 574         raise TypeError(msg)
      575 
      576     def _search_new_conversions(self, *args, **kws):
  
  TypeError: No matching definition for argument type(s) array(float64, 2d, C), array(int32, 1d, C), array(bool, 1d, C)
  ```
  I haven't change anything in the code.
  Looks like numba error?