Changed script for Travis CI

Author: Denis Ivanov

.travis.yml

@@ -2,6 +2,6 @@ language: csharp
 solution: src/AngleSharp.XPath.sln
 dotnet  : 2.0.3
 script  :
-  - dotnet restore
-  - dotnet build
+  - dotnet restore src/AngleSharp.XPath.sln
+  - dotnet build src/AngleSharp.XPath.sln
   - dotnet test ./**/*Tests/