Fix typo in original commit

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>

CMakeLists.txt

@@ -227,7 +227,7 @@ if (USE_GIT_DESCRIBE OR CHECK_GIT_TAG)
 endif()
 message ("-- Build tag is '${BUILD_TAG}'")
 if (NOT "${BASE_BUILD_TAG}" STREQUAL "")
-    set(BUILD_TAG "${BUILD_TAG}[)
+    set(BASE_BUILD_TAG "${BUILD_TAG}")
 endif()
 message ("-- Base build tag is '${BASE_BUILD_TAG}'")
 configure_file(${HPCC_SOURCE_DIR}/build-config.h.cmake "build-config.h" )