Correct grammar in current_{cpu,os} docs

Change-Id: I32daf9161f33ad0613d2d3ee0913e51f16cde54d
Reviewed-on: https://gn-review.googlesource.com/2140
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
diff --git a/tools/gn/docs/reference.md b/tools/gn/docs/reference.md
index 3f55566..b8169cd 100644
--- a/tools/gn/docs/reference.md
+++ b/tools/gn/docs/reference.md
@@ -3398,7 +3398,7 @@
   toolchain definitions to ensure that it always reflects the appropriate
   value.
 
-  This value is not used internally by GN for any purpose. It is set it to the
+  This value is not used internally by GN for any purpose. It is set to the
   empty string ("") by default but is declared so that it can be overridden on
   the command line if so desired.
 
@@ -3412,7 +3412,7 @@
   toolchain definitions to ensure that it always reflects the appropriate
   value.
 
-  This value is not used internally by GN for any purpose. It is set it to the
+  This value is not used internally by GN for any purpose. It is set to the
   empty string ("") by default but is declared so that it can be overridden on
   the command line if so desired.
 
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index b30c0b6..c286408 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -207,7 +207,7 @@
   toolchain definitions to ensure that it always reflects the appropriate
   value.
 
-  This value is not used internally by GN for any purpose. It is set it to the
+  This value is not used internally by GN for any purpose. It is set to the
   empty string ("") by default but is declared so that it can be overridden on
   the command line if so desired.
 
@@ -224,7 +224,7 @@
   toolchain definitions to ensure that it always reflects the appropriate
   value.
 
-  This value is not used internally by GN for any purpose. It is set it to the
+  This value is not used internally by GN for any purpose. It is set to the
   empty string ("") by default but is declared so that it can be overridden on
   the command line if so desired.