Add android tools environment to gitignore

Previously, if you did `make envpaths` (as described in README.android), the new file got listed by git as new file.

.gitignore

@@ -92,6 +92,7 @@ build/android/jni/src
 build/android/libs
 build/android/obj
 build/android/path.cfg
+build/android/and_env
 build/android/AndroidManifest.xml
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