Fix always-empty value for $DOT_GIT_DIR variable.

This fixes #53.

gitflow-common

@@ -181,7 +181,7 @@ gitflow_is_initialized() {
 
 # loading settings that can be overridden using git config
 gitflow_load_settings() {
-	export DOT_GIT_DIR=$(git rev-parse --git-dir >/dev/null 2>&1)
+	export DOT_GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
 	export MASTER_BRANCH=$(git config --get gitflow.branch.master)
 	export DEVELOP_BRANCH=$(git config --get gitflow.branch.develop)
 	export ORIGIN=$(git config --get gitflow.origin || echo origin)