switch to clang-format-3.8 (#2547)

https://llvm.org/bugs/show_bug.cgi?id=30353 was filed for the unintended
line break between in e.g. “TAILQ_ENTRY(foo)\nbar;”.

Until that’s fixed or a workaround is known, we’ll live with line
breaks. To make it a bit easier for readers to see what’s going on, I
added extra line breaks around each such struct member/variable
definition, so that they at least visually are a single unit.

fixes #2174

i3bar/include/common.h

@@ -74,10 +74,12 @@ struct status_block {
     char *name;
     char *instance;
 
-    TAILQ_ENTRY(status_block) blocks;
+    TAILQ_ENTRY(status_block)
+    blocks;
 };
 
-TAILQ_HEAD(statusline_head, status_block) statusline_head;
+TAILQ_HEAD(statusline_head, status_block)
+statusline_head;
 
 #include "child.h"
 #include "ipc.h"