fix: remove extra spaces in error message leading to invalid path

[jim-bcom]

Remove extra space after 'cd' command
Remove extra space in built path, resulting in an invalid path

Error message before:

: -1: error: Project ERROR: cppast root build folder doesn't exist: create cppast root build folder and build cppast prior to running qmake.
To build cppast do :
cd  /home/user/work/xpcf/xpcf/tools/generators/grpc /../../../libs/
./build_cppast.sh

Error message after:

:  -1: error: Project ERROR: cppast root build folder doesn't exist: create cppast root build folder and build cppast prior to running qmake.
To build cppast do :
cd /home/user/work/xpcf/xpcf/tools/generators/grpc/../../../libs/
./build_cppast.sh