Build failure with current libosmium

[robinhouston]

I was seeing a build failure against HEAD libosmium, with the first error being:

[ 10%] Building CXX object CMakeFiles/osmcoastline.dir/coastline_ring.cpp.o
In file included from /Users/robin/osmcoastline/coastline_ring.cpp:26:
/Users/robin/osmcoastline/coastline_ring.hpp:64:10: error: no type named 'vector' in namespace 'std'
    std::vector<osmium::NodeRef> m_way_node_list;
    ~~~~~^

The following patch – which may not be the best fix – makes it work:

diff --git a/coastline_ring.hpp b/coastline_ring.hpp
index 80f3c29..585a4e4 100644
--- a/coastline_ring.hpp
+++ b/coastline_ring.hpp
@@ -24,6 +24,7 @@

 #include <map>
 #include <memory>
+#include <vector>

 #include <osmium/geom/ogr.hpp>
 #include <osmium/osm/undirected_segment.hpp>