Refactor: rename namespace witherspoon to phosphor

This repo now becomes phosphor-power, rename namespace witherspoon to
phosphor to make it generic.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: Icb9f8a7c33065add99f2bf42ed55745a28fa0424
diff --git a/power-supply/argument.cpp b/power-supply/argument.cpp
index 342515c..7b671d8 100644
--- a/power-supply/argument.cpp
+++ b/power-supply/argument.cpp
@@ -20,7 +20,7 @@
 #include <iostream>
 #include <iterator>
 
-namespace witherspoon
+namespace phosphor
 {
 namespace power
 {
@@ -99,4 +99,4 @@
 const std::string ArgumentParser::emptyString = "";
 
 } // namespace power
-} // namespace witherspoon
+} // namespace phosphor