fix vs2015 solution

Author: cbovar

src/ConvNetSharp.Flow/ConvNetSharp.Flow.2015.csproj

@@ -21,6 +21,7 @@
     <DefineConstants>DEBUG;TRACE</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
+    <LangVersion>6</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugType>pdbonly</DebugType>

src/ConvNetSharp.Flow/Layers/ConvLayer.cs

@@ -25,7 +25,7 @@ public ConvLayer(int width, int height, int filterCount)
 
         public T BiasPref
         {
-            get => this._biasPref;
+            get { return this._biasPref; }
             set
             {
                 this._biasPref = value;
@@ -39,7 +39,7 @@ public T BiasPref
 
         public int Stride
         {
-            get => this._stride;
+            get { return this._stride; }
             set
             {
                 this._stride = value;
@@ -52,7 +52,7 @@ public int Stride
 
         public int Pad
         {
-            get => this._pad;
+            get { return this._pad; }
             set
             {
                 this._pad = value;

src/ConvNetSharp.Flow/Layers/PoolLayer.cs

@@ -20,7 +20,7 @@ public PoolLayer(int width, int height)
 
         public int Stride
         {
-            get => this._stride;
+            get { return this._stride; }
             set
             {
                 this._stride = value;
@@ -34,7 +34,7 @@ public int Stride
 
         public int Pad
         {
-            get => this._pad;
+            get { return this._pad; }
             set
             {
                 this._pad = value;