Fails to build with cpputest 3.8

[MitchellThompkins]

When building with cpputest 3.8 the output is:

[ 20%] Built target LedDriver
[ 40%] Built target Tutorial
[ 60%] Built target RuntimeErrorStub
[ 80%] Built target LedDriverTest
make[2]: *** No rule to make target `/Users/timothythompkins/_git/cpputest/src/CppUTest/libCppUTest.a', needed by `bin/RunAllTests'.  Stop.
make[1]: *** [tests/CMakeFiles/RunAllTests.dir/all] Error 2
make: *** [all] Error 2

This is due to this line:

cmake-cpputest/tests/CMakeLists.txt

Line 16 in 85f410f

IMPORTED_LOCATION $ENV{CPPUTEST_HOME}/src/CppUTest/libCppUTest.a)

Pointing to the correct lib location below fixes this issue.

 IMPORTED_LOCATION $ENV{CPPUTEST_HOME}/lib/libCppUTest.a)