docs: fix misspellings

Fixed what I noticed; no warranty for exhaustiveness.

Signed-off-by: Nathan Kidd <nkidd@opentext.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
diff --git a/docs/sourcetree.html b/docs/sourcetree.html
index a6868d3..4c93f63 100644
--- a/docs/sourcetree.html
+++ b/docs/sourcetree.html
@@ -123,7 +123,7 @@
           Currently there's run-time code generation for x86/SSE, PowerPC
           and Cell SPU.
       <li><b>tgsi</b> - TG Shader Infrastructure.  Code for encoding,
-          manipulating and interpretting GPU programs.
+          manipulating and interpreting GPU programs.
       <li><b>translate</b> - module for translating vertex data from one format
           to another.
       <li><b>util</b> - assorted utilities for arithmetic, hashing, surface