fix alloc-dealloc-mismatch for _storage.str.data

[alsora]

The variable _storage.str.data is a char* allocated as

_storage.str.data = new char[size + 1];

This means that we should use delete[] to deallocate it, to avoid undefined behavior.

[alsora]

One of the jobs failed with the following error which seems unrelated

  Errors     << behaviortree_cpp:make /root/target_ws/logs/behaviortree_cpp/test.make.000.log
  /usr/bin/ld: /usr/lib/x86_64-linux-gnu/libgtest.a(gtest-all.cc.o): undefined reference to symbol 'pthread_getspecific@@GLIBC_2.2.5'
  /usr/bin/ld: /lib/x86_64-linux-gnu/libpthread.so.0: error adding symbols: DSO missing from command line
  collect2: error: ld returned 1 exit status
  make[3]: *** [tests/CMakeFiles/behaviortree_cpp_test.dir/build.make:350: /root/target_ws/devel/.private/behaviortree_cpp/lib/behaviortree_cpp/behaviortree_cpp_test] Error 1
  make[2]: *** [CMakeFiles/Makefile2:742: tests/CMakeFiles/behaviortree_cpp_test.dir/all] Error 2
  make[1]: *** [CMakeFiles/Makefile2:476: CMakeFiles/run_tests.dir/rule] Error 2
  make: *** [Makefile:253: run_tests] Error 2
  cd /root/target_ws/build/behaviortree_cpp; catkin test --get-env behaviortree_cpp | catkin env -si  /usr/bin/make run_tests; cd -

[facontidavide]

thanks