less-parser: Handle edge case with single token mixins. (#80)

* less-parser: Handle edge case with single token mixins.

The parser didn't account for mixins that were used in the following manner:

```
.foo {.my-mixin}
```

* tests: Use to.be.undefined in assertion.

Author: ymichael

lib/less-parser.js

@@ -321,6 +321,11 @@ export default class LessParser extends Parser {
 
     // dont process an end of rule if there's only one token and it's unknown (#64)
     if (end && this.tokens.length > 1) {
+      // Handle the case where the there is only a single token in the end rule.
+      if (start === this.pos) {
+        this.pos += 1;
+      }
+
       const foundEndOfRule = this.ruleEnd({
         start,
         params,

test/parser/mixins.spec.js

@@ -36,9 +36,19 @@ describe('Parser', () => {
 
         expect(root.first.first.type).to.eql('rule');
         expect(root.first.first.selector).to.eql('.mixin-name');
-        expect(root.first.params).to.be.an('undefined');
+        expect(root.first.params).to.be.undefined;
         expect(root.first.first.empty).to.eql(true);
-        expect(root.first.first.nodes).to.be.an('undefined');
+        expect(root.first.first.nodes).to.be.undefined;
+      });
+
+      it('mixin without body and without whitespace #2', () => {
+        const root = parse('.base {.mixin-name}');
+
+        expect(root.first.first.type).to.eql('rule');
+        expect(root.first.first.selector).to.eql('.mixin-name');
+        expect(root.first.params).to.be.undefined;
+        expect(root.first.first.empty).to.eql(true);
+        expect(root.first.first.nodes).to.be.undefined;
       });
     });