Add support for netstandard1.3

Author: dmirmilshteyn

.gitignore

@@ -5,6 +5,7 @@
 *.suo
 *.user
 *.sln.docstates
+.vs/
 
 # Build results
 [Dd]ebug/

.travis.yml

@@ -1,12 +1,6 @@
 language: csharp
 solution: prometheus-net.sln
 install:
-  - nuget restore prometheus-net.sln
-  - nuget install NUnit.Runners -Version 3.0.1 -OutputDirectory testrunner
+  - dotnet restore prometheus-net.sln
 script:
-  - xbuild /p:Configuration=Release prometheus-net.sln
-  - ls -la
-  - ls -la testrunner
-  - find . -name "prometheus-net.tests.dll"
-  - mono ./testrunner/NUnit.Console.3.0.1/tools/nunit3-console.exe ./prometheus-net.NET40.tests/bin/Release/prometheus-net.tests.dll
-  - mono ./testrunner/NUnit.Console.3.0.1/tools/nunit3-console.exe ./prometheus-net.NET45.tests/bin/Release/prometheus-net.tests.dll
+  - dotnet test --configuration Release "prometheus-net.tests/prometheus-net.tests.csproj"

GlobalAssemblyInfo.cs

@@ -1,5 +1,3 @@
 set version=%1
 ::todo: use FAKE 
-::C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild prometheus-net.sln /p:Configuration=Release
-"C:\Program Files (x86)\MSBuild\14.0\Bin\msbuild" prometheus-net.sln /p:Configuration=Release
-nuget pack prometheus-net.nuspec -properties version="%version%"
+dotnet pack prometheus-net/prometheus-net.csproj --configuration Release /p:Version="%version%"