Clean sample code biorhythm (#2375)

* Standardize to load date libary code

> git grep 'require .date.' | wc -l
179
> git grep 'require .date\.rb' | wc -l
1

* Simplify

1 files changed, 4 insertions, 5 deletions

diff --git a/sample/biorhythm.rb b/sample/biorhythm.rb
index bd7c39f5aa..f5d189014b 100644
--- a/sample/biorhythm.rb
+++ b/sample/biorhythm.rb
@@ -25,7 +25,7 @@
 # Environment: basic, dos, os9
 
 include Math
-require "date.rb"
+require "date"
 require "optparse"
 require "optparse/date"
 
@@ -36,11 +36,10 @@ def print_header(y, m, d, p, w)
 end
 
 def get_position(z)
-  pi = Math::PI
   z = Integer(z)
-  phys = (50.0 * (1.0 + sin((z / 23.0 - (z / 23)) * 360.0 * pi / 180.0))).to_i
-  emot = (50.0 * (1.0 + sin((z / 28.0 - (z / 28)) * 360.0 * pi / 180.0))).to_i
-  geist =(50.0 * (1.0 + sin((z / 33.0 - (z / 33)) * 360.0 * pi / 180.0))).to_i
+  phys = (50.0 * (1.0 + sin((z / 23.0 - (z / 23)) * 360.0 * PI / 180.0))).to_i
+  emot = (50.0 * (1.0 + sin((z / 28.0 - (z / 28)) * 360.0 * PI / 180.0))).to_i
+  geist =(50.0 * (1.0 + sin((z / 33.0 - (z / 33)) * 360.0 * PI / 180.0))).to_i
   return phys, emot, geist
 end