Fix formatting of CodingConventions.md.

The current page has some issue:

https://gitlab.kitware.com/vtk/vtk-m/blob/master/docs/CodingConventions.md

docs/CodingConventions.md

@@ -15,7 +15,7 @@ coding and because we expect vtkm to have continual interaction with VTK.
     form. Various copyright specific details are referenced in the LICENSE.txt
     file.
 
-    ```
+```
 //==========================================================================
 //  Copyright (c) Kitware, Inc.
 //  All rights reserved.
@@ -25,7 +25,7 @@ coding and because we expect vtkm to have continual interaction with VTK.
 //  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 //  PURPOSE.  See the above copyright notice for more information.
 //==========================================================================
-    ```
+```
 
   + The CopyrightStatement test checks all files for a similar statement.
     The test will print out a suggested text that can be copied and pasted
@@ -41,22 +41,21 @@ coding and because we expect vtkm to have continual interaction with VTK.
     directory, with non alphanumeric characters, such as / and . replaced
     with underscores. The `#endif` part of the guard at the bottom of the
     file should include the guard name in a comment. For example, the
-    vtkm/cont/ArrayHandle.h header contains the guard
-
-    ```cpp
-  #ifndef vtk_m_cont_ArrayHandle_h
-  #define vtk_m_cont_ArrayHandle_h
-    ```
-    at the top and
-    ```cpp
-  #endif //vtk_m_cont_ArrayHandle_h
-    ```
-    at the bottom.
+    vtkm/cont/ArrayHandle.h header contains the guard demostrated below.
 
     The unique use of vtk_m over vtkm is to allow auto-complete engines the
     ability to differentiate between the header guards and VTKM_ macros
     that are used within the code base.
 
+```cpp
+#ifndef vtk_m_cont_ArrayHandle_h
+#define vtk_m_cont_ArrayHandle_h
+
+// All ArrayHandle code here
+
+#endif //vtk_m_cont_ArrayHandle_h
+```
+
   + The VTK-m toolkit has several nested namespaces. The declaration of
     each namespace should be on its own line, and the code inside the
     namespace bracket should not be indented. The closing brace at the
@@ -64,7 +63,7 @@ coding and because we expect vtkm to have continual interaction with VTK.
     the namespace. Namespaces can be grouped as desired. The following is a
     valid use of namespaces.
 
-    ```cpp
+```cpp
 namespace vtkm {
 namespace cont {
 namespace detail {
@@ -73,7 +72,7 @@ class InternalClass;
 class ExposedClass;
 }
 } // namespace vtkm::cont
-    ```
+```
 
   + Multiple inheritance is not allowed in VTK-m classes.
 
@@ -170,7 +169,7 @@ for (auto v : vector)
     or detail class clearly associated with it, the reference can be
     shortened to `internal::` or `detail::`.
 
-  + use `this->` inside of methods when accessing class methods and
+  + Use `this->` inside of methods when accessing class methods and
     instance variables to distinguish between local variables and instance
     variables.