doc: remove overflowing literals

It was a copy & paste error.

Fixes #123
diff --git a/src/lib.rs b/src/lib.rs
index 63d5170..54ce786 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1197,7 +1197,7 @@
     /// use byteorder::{ByteOrder, LittleEndian};
     ///
     /// let mut bytes = [0; 16];
-    /// let numbers_given = [1.0, 2.0, 31.312e311, -11.32e91];
+    /// let numbers_given = [1.0, 2.0, 31.312e31, -11.32e19];
     /// LittleEndian::write_f32_into(&numbers_given, &mut bytes);
     ///
     /// let mut numbers_got = [0.0; 4];
@@ -1463,7 +1463,7 @@
     /// use byteorder::{ByteOrder, LittleEndian};
     ///
     /// let mut bytes = [0; 16];
-    /// let numbers_given = [1.0, 2.0, 31.312e311, -11.32e91];
+    /// let numbers_given = [1.0, 2.0, 31.312e31, -11.32e19];
     /// LittleEndian::write_f32_into(&numbers_given, &mut bytes);
     ///
     /// let mut numbers_got = [0.0; 4];