Fix cmake warning about newlines

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

Author: scpeters

Changelog.md

@@ -4,6 +4,9 @@
 
 ### libsdformat 10.0.0 (202X-XX-XX)
 
+1. Don't install deprecated parser_urdf.hh header file, fix cmake warning about newline file, fix cmake warning about newlines.
+    * [Pull request 276](https://github.com/osrf/sdformat/pull/276)
+
 1. Changed the default radius of a Cylinder from 1.0 to 0.5 meters.
     * [BitBucket pull request 643](https://osrf-migration.github.io/sdformat-gh-pages/#!/osrf/sdformat/pull-requests/643)
 

include/sdf/CMakeLists.txt

@@ -49,8 +49,7 @@ set (headers
 
 set (sdf_headers "" CACHE INTERNAL "SDF headers" FORCE)
 foreach (hdr ${headers})
-  APPEND_TO_CACHED_STRING(sdf_headers
-    "SDF Headers" "#include <sdf/${hdr}>\n")
+  set(sdf_headers "${sdf_headers}#include <sdf/${hdr}>\n")
 endforeach()
 configure_file (${CMAKE_CURRENT_SOURCE_DIR}/sdf.hh.in
                 ${CMAKE_CURRENT_BINARY_DIR}/sdf.hh)