Add mastodon handle to all Yusuke Endoh entries

This was easy with my sgit tool which I didn't think about until shortly
after the previous commit (20edd11936).

2015/endoh1/README.md

@@ -1,11 +1,11 @@
 # Most Diffused Reaction
 
-    Yusuke Endoh  
-    <https://github.com/mame/>  
-    Twitter: @mametter  
+Yusuke Endoh  
+<https://github.com/mame/>  
+Mastodon: [@mame@ruby.social](https://ruby.social/@mame)  
 
-    Someone Anonymous  
-    Twitter: @hirekoke  
+Someone Anonymous  
+Twitter: @hirekoke  
 
 ## To build:
 

2015/endoh2/README.md

@@ -1,8 +1,8 @@
 # Most Overlooked Obfuscation
 
-    Yusuke Endoh  
-    <https://github.com/mame/>  
-    Twitter: @mametter  
+Yusuke Endoh    
+<https://github.com/mame/>  
+Mastodon: [@mame@ruby.social](https://ruby.social/@mame)  
 
 ## To build:
 

2015/endoh3/README.md

@@ -2,7 +2,7 @@
 
 Yusuke Endoh  
 <https://github.com/mame/>  
-Twitter: @mametter  
+Mastodon: [@mame@ruby.social](https://ruby.social/@mame)  
 
 ## To build:
 

2015/endoh4/README.md

@@ -2,7 +2,7 @@
 
 Yusuke Endoh  
 <https://github.com/mame/>  
-Twitter: @mametter  
+Mastodon: [@mame@ruby.social](https://ruby.social/@mame)  
 
 ## To build: