Do not use sed -E in bootstrap/compile.sh

Strangely enough, some clients have sed that doesn't support -E

RELNOTES: None.
PiperOrigin-RevId: 157397892
diff --git a/scripts/bootstrap/compile.sh b/scripts/bootstrap/compile.sh
index 6facda2..ce24d1a 100755
--- a/scripts/bootstrap/compile.sh
+++ b/scripts/bootstrap/compile.sh
@@ -67,8 +67,8 @@
 
 function get_minor_java_version() {
   get_java_version
-  java_minor_version=$(echo $JAVA_VERSION | sed -E 's/.+\.(.+)(\..*)?/\1/')
-  javac_minor_version=$(echo $JAVAC_VERSION | sed -E 's/.+\.(.+)(\..*)?/\1/')
+  java_minor_version=$(echo $JAVA_VERSION | sed 's/[^.][^.]*\.//' | sed 's/\..*$//')
+  javac_minor_version=$(echo $JAVAC_VERSION | sed 's/[^.][^.]*\.//' | sed 's/\..*$//')
 }
 
 # Check that javac -version returns a upper version than $JAVA_VERSION.