missing word: "block"

Author: nikomatsakis

Diff for: src/background.md

@@ -17,9 +17,9 @@ A control-flow graph is structured as a set of **basic blocks**
 connected by edges. The key idea of a basic block is that it is a set
 of statements that execute "together" -- that is, whenever you branch
 to a basic block, you start at the first statement and then execute
-all the remainder. Only at the end of the is there the possibility of
-branching to more than one place (in MIR, we call that final statement
-the **terminator**):
+all the remainder. Only at the end of the block is there the
+possibility of branching to more than one place (in MIR, we call that
+final statement the **terminator**):
 
 ```
 bb0: {