Fix typos (#103)

Author: kianmeng

readthedocs_ext/external_version_warning.py

@@ -1,7 +1,7 @@
 from docutils import nodes
 
 try:
-    # Avaliable from Sphinx 1.6
+    # Available from Sphinx 1.6
     from sphinx.util.logging import getLogger
 except ImportError:
     from logging import getLogger

readthedocs_ext/readthedocs.py

@@ -18,7 +18,7 @@
 from .embed import EmbedDirective
 
 try:
-    # Avaliable from Sphinx 1.6
+    # Available from Sphinx 1.6
     from sphinx.util.logging import getLogger
 except ImportError:
     from logging import getLogger

readthedocs_ext/versionwarning.py

@@ -22,7 +22,7 @@
 from docutils import nodes
 
 try:
-    # Avaliable from Sphinx 1.6
+    # Available from Sphinx 1.6
     from sphinx.util.logging import getLogger
 except ImportError:
     from logging import getLogger