Merge pull request scikit-learn#5117 from kylerbrown/patch-1

fixing a typo in feature extraction documentation

doc/modules/feature_extraction.rst

@@ -398,7 +398,7 @@ suitable for usage by a classifier it is very common to use the tf–idf
 transform.
 
 Tf means **term-frequency** while tf–idf means term-frequency times
-**inverse document-frequency**. This is a originally a term weighting
+**inverse document-frequency**. This was originally a term weighting
 scheme developed for information retrieval (as a ranking function
 for search engines results), that has also found good use in document
 classification and clustering.