Fix typo in newsletters; thanks Steve Lee for reporting

Author: harding

_posts/en/newsletters/2018-07-31-newsletter.md

@@ -85,7 +85,7 @@ C-lightning projects.
 https://bitcoin.stackexchange.com/search?tab=votes&q=created%3a1m..%20is%3aanswer
 -->{% endcomment %}
 
-*[Bitcoin StackExachange][bitcoin.se] is one of the first places Optech
+*[Bitcoin StackExchange][bitcoin.se] is one of the first places Optech
 contributors look for answers to their questions---or when we have a
 few spare moments of time to help answer other people's questions.  In
 this new monthly feature, we highlight some of the top voted questions

_posts/en/newsletters/2018-08-28-newsletter.md

@@ -67,7 +67,7 @@ infrastructure projects.
 
 {% comment %}<!-- https://bitcoin.stackexchange.com/search?tab=votes&q=created%3a1m..%20is%3aanswer -->{% endcomment %}
 
-*[Bitcoin StackExachange][bitcoin.se] is one of the first places Optech
+*[Bitcoin StackExchange][bitcoin.se] is one of the first places Optech
 contributors look for answers to their questions---or when we have a
 few spare moments of time to help answer other people's questions.  In
 this monthly feature, we highlight some of the top voted questions and