[range.istream.view] Fix missing ranges:: qualifier in example (#4296)

Author: miscco

source/ranges.tex

@@ -2751,7 +2751,7 @@
 \begin{example}
 \begin{codeblock}
 auto ints = istringstream{"0 1  2   3     4"};
-ranges::copy(istream_view<int>(ints), ostream_iterator<int>{cout, "-"});
+ranges::copy(ranges::istream_view<int>(ints), ostream_iterator<int>{cout, "-"});
 // prints \tcode{0-1-2-3-4-}
 \end{codeblock}
 \end{example}