Tilde to caret normalization issue for pre-1.0 versions

Currently normalizer does this:
```
-    "foo/bar": "~0.1"
+    "foo/bar": "^0.1"
```

This is wrong because 
~0.1 evaluates to >=0.1 <1.0 
however 
^0.1 evalueates to >=0.1 <0.2