docs(guide/unit-testing): fix small typo (than instead of then)

Author: lefos987

docs/content/guide/unit-testing.ngdoc

@@ -96,7 +96,7 @@ function MyClass() {
 ```
 
 While no new dependency instance is created, it is fundamentally the same as `new` in
-that no  way exists to intercept the call to `global.xhr` for testing purposes, other then
+that no  way exists to intercept the call to `global.xhr` for testing purposes, other than
 through monkey patching. The basic issue for testing is that a global variable needs to be mutated in
 order to replace it with call to a mock method. For further explanation of why this is bad see: [Brittle Global
 State & Singletons](http://misko.hevery.com/code-reviewers-guide/flaw-brittle-global-state-singletons/)