Fix typo

Author: GuillaumeGomez

src/librustdoc/html/render/span_map.rs

@@ -36,7 +36,7 @@ pub(crate) enum LinkFromSrc {
 /// It returns the `krate`, the source code files and the `span` correspondence map.
 ///
 /// Note about the `span` correspondence map: the keys are actually `(lo, hi)` of `span`s. We don't
-/// need the `span` context later on, only their position, so instead of keep a whole `Span`, we
+/// need the `span` context later on, only their position, so instead of keeping a whole `Span`, we
 /// only keep the `lo` and `hi`.
 pub(crate) fn collect_spans_and_sources(
     tcx: TyCtxt<'_>,