correct size of default memory map

src/environment.rs

@@ -316,7 +316,7 @@ impl EnvironmentBuilder {
     /// Sets the size of the memory map to use for the environment.
     ///
     /// The size should be a multiple of the OS page size. The default is
-    /// 10485760 bytes. The size of the memory map is also the maximum size
+    /// 1048576 bytes. The size of the memory map is also the maximum size
     /// of the database. The value should be chosen as large as possible,
     /// to accommodate future growth of the database. It may be increased at
     /// later times.