minor spell fix (#2601)

examples/02-data-processing.ipynb

@@ -19,7 +19,7 @@
     "\n",
     "`DataTransformer` aims to provide a unified way of dealing with transformations of `TimeSeries`:\n",
     "\n",
-    "- `transform()` is implemented by all transformers. This method takes in either a `TimeSeries` of a sequence of `TimeSeries`, applies the transformation and returns it as a new `TimeSeries`/sequence of `TimeSeries.\n",
+    "- `transform()` is implemented by all transformers. This method takes in either a `TimeSeries` or a sequence of `TimeSeries`, applies the transformation and returns it as a new `TimeSeries`/sequence of `TimeSeries.\n",
     "- `inverse_transform()` is implemented by transformers for which an inverse transformation function exists. It works in a similar way as `transform()`\n",
     "- `fit()` allows transformers to extract some information from the time series first before calling `transform()` or `inverse_transform()`\n"
    ]