lg2: missing include for ranges::find

The lg2/header.hpp used ranges::find but didn't include the
defining header file (algorithm).  This was probably missed
because in many cases algorithm is pulled in as a dependency
from other STL headers, but if you make an empty file with
nothing except 'include <phosphor-logging/lg2.hpp>' the function
definition is missing.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I64cd7edcacaccb02b15904486010c3bce5c28dba
diff --git a/lib/include/phosphor-logging/lg2/header.hpp b/lib/include/phosphor-logging/lg2/header.hpp
index 831bfc1..dbe84ce 100644
--- a/lib/include/phosphor-logging/lg2/header.hpp
+++ b/lib/include/phosphor-logging/lg2/header.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <algorithm>
 #include <array>
 #include <phosphor-logging/lg2/concepts.hpp>
 #include <string_view>