Fix grammar in blog posts

Author: spikefoo

src/pages/blog/compiler-errors-for-humans.elm

@@ -153,7 +153,7 @@ happening.** When reading a technical text, it is always easier if the author
 has defined the terms they are using and the specific issue they are
 addressing. It makes the details much more concrete.
 
-Again, lets look at how the Elm 0.15.1 messages use these observations to
+Again, let's look at how the Elm 0.15.1 messages use these observations to
 improve error messages. This example tries to make a list of user pictures, but
 we mix up HTML and raw strings.
 

src/pages/blog/making-pong.elm

@@ -51,7 +51,7 @@ The structure of Elm games breaks into four major parts: modeling inputs,
 modeling the game, updating the game, and viewing the game. It may be helpful
 to think of it as a functional variation on the Model-View-Controller paradigm.
 
-To make this more concrete, lets see how Pong needs to be structured:
+To make this more concrete, let's see how Pong needs to be structured:
 
  1. [**Inputs**](#inputs) — This is all of the stuff coming in from
     “the world”. For Pong, this is keyboard input from users and