Change reference to IlmBase to Imath in README.md
I really thought we'd eradicated references to IlmBase, but apparently not.
@@ -136,8 +136,8 @@ OpenEXR is intended solely for 2D data. It is not appropriate for
storage of volumetric data, cached or lit 3D scenes, or more complex
3D data such as light fields.
-The goals of the IlmBase project are simplicity, ease of use,
-correctness and verifiability, and breadth of adoption. IlmBase is not
+The goals of the Imath project are simplicity, ease of use,
+correctness and verifiability, and breadth of adoption. Imath is not
intended to be a comprehensive linear algebra or numerical analysis
package.
