Typo fixes in comments

Signed-off-by: Kartik Mistry <kartik.mistry@gmail.com>

hy/__main__.py

@@ -23,7 +23,7 @@ import imp
 import sys
 
 # This just mocks the normalish behavior of the Python interp. Helpful to aid
-# with shiming existing apps that don't really "work" with Hy.
+# with shimming existing apps that don't really "work" with Hy.
 #
 # You could say this script helps Hyjack a file.
 #

hy/compiler.py

@@ -1512,7 +1512,7 @@ class HyASTCompiler(object):
     def compile_require(self, expression):
         """
         TODO: keep track of what we've imported in this run and then
-        "unimport" it after we've completed `thing' so that we don't polute
+        "unimport" it after we've completed `thing' so that we don't pollute
         other envs.
         """
         expression.pop(0)

hy/errors.py

@@ -28,7 +28,7 @@ import traceback
 
 class HyError(Exception):
     """
-    Generic Hy error. All interal Exceptions will be subclassed from this
+    Generic Hy error. All internal Exceptions will be subclassed from this
     Exception.
     """
     pass