[range.req.general] Fix grammar typo

Author: jensmaurer

source/ranges.tex

@@ -1090,7 +1090,7 @@
 \rSec2[range.req.general]{General}
 
 \pnum
-Ranges are an abstraction that allow a \Cpp{} program
+Ranges are an abstraction that allows a \Cpp{} program
 to operate on elements of data structures uniformly.
 Calling \tcode{ranges::begin} on a range returns an object
 whose type models \libconcept{input_or_output_iterator}\iref{iterator.concept.iterator}.