Default to ^ operator on --save

This fix brings us inline with how npm installs work and also brings us
more inline with how semver is supposed to be used.

Fixes #2144

lib/core/Manager.js

@@ -595,7 +595,7 @@ Manager.prototype._dissect = function () {
         // If they are not, the resolver is incapable of handling targets
         semvers.forEach(function (decEndpoint) {
             if (decEndpoint.newly && decEndpoint.target === '*' && !decEndpoint.untargetable) {
-                decEndpoint.target = '~' + decEndpoint.pkgMeta.version;
+                decEndpoint.target = '^' + decEndpoint.pkgMeta.version;
                 decEndpoint.originalTarget = '*';
             }
         });