In ajax.js: Update tests to validate content not just of type string

[juwara0]

In ajax.js: Update tests to validate the content not just that it is of type string for the lines below:

sl-ember-store/tests/unit/adapters/ajax-test.js

Line 184 in 0d91357

assert.equal( typeof requestSpy.args[0][0].data, 'string', 'icAjax should return a string');

sl-ember-store/tests/unit/adapters/ajax-test.js

Line 193 in 0d91357

assert.equal( typeof requestSpy.args[0][0].data, 'string' );

sl-ember-store/tests/unit/adapters/ajax-test.js

Line 204 in 0d91357

assert.equal( typeof requestSpy.args[0][0].data, 'string', 'icAjax should return a string');