Shorten some excessively long lines of CMake (#300)

The line length enforcement in ament_lint_cmake has been broken for some
time, but will be fixed by ament/ament_lint#236. This change brings this
package into compliance with a 120 column limit.

Signed-off-by: Scott K Logan <logans@cottsay.net>

Author: cottsay

rmw_implementation_cmake/cmake/get_default_rmw_implementation.cmake

@@ -57,7 +57,9 @@ macro(get_default_rmw_implementation var)
   list(FIND _middleware_implementations "${_middleware_implementation}" _index)
   if(_index EQUAL -1)
     string(REPLACE ";" ", " _middleware_implementations_string "${_middleware_implementations}")
-    message(FATAL_ERROR "Could not find ROS middleware implementation '${_middleware_implementation}'. Choose one of the following: ${_middleware_implementations_string}")
+    message(FATAL_ERROR
+      "Could not find ROS middleware implementation '${_middleware_implementation}'. "
+      "Choose one of the following: ${_middleware_implementations_string}")
   endif()
   find_package("${_middleware_implementation}" REQUIRED)