Fixing nvm_version_greater tests.

Relates to #505, #506.

test/fast/Unit tests/nvm_version_greater

@@ -5,6 +5,12 @@ die () { echo $@ ; exit 1; }
 . ../../../nvm.sh
 
 nvm_version_greater 0.10.0 0.2.12 || die '"nvm_version_greater 0.10.0 0.2.12" did not return true'
-nvm_version_greater 0.10.0 0.20.12 && die '"nvm_version_greater 0.10.0 0.20.12" returned true'
+
-nvm_version_greater 0.10.0 0.10.0 && die '"nvm_version_greater" returned false for the same two versions'
+if nvm_version_greater 0.10.0 0.20.12; then
+  die '"nvm_version_greater 0.10.0 0.20.12" returned true'
+fi
+
+if nvm_version_greater 0.10.0 0.10.0; then
+  die '"nvm_version_greater" returned false for the same two versions'
+fi