Fix typos in comments

Change-Id: I17faeb9b9a4cd40de7651eea3ff011e48910f059

internal/ceres/block_jacobian_writer.cc

diff --git a/internal/ceres/block_jacobian_writer.cc b/internal/ceres/block_jacobian_writer.cc
index 8b77f1d..5a769cb 100644
--- a/internal/ceres/block_jacobian_writer.cc
+++ b/internal/ceres/block_jacobian_writer.cc
@@ -178,7 +178,7 @@
                                                   &jacobian_layout_storage_);
 }
 
-// Create evaluate prepareres that point directly into the final jacobian. This
+// Create evaluate preparers that point directly into the final jacobian. This
 // makes the final Write() a nop.
 std::unique_ptr<BlockEvaluatePreparer[]>
 BlockJacobianWriter::CreateEvaluatePreparers(unsigned num_threads) {

internal/ceres/block_jacobian_writer.h

diff --git a/internal/ceres/block_jacobian_writer.h b/internal/ceres/block_jacobian_writer.h
index 31e35ac..a6d02e3 100644
--- a/internal/ceres/block_jacobian_writer.h
+++ b/internal/ceres/block_jacobian_writer.h
@@ -68,7 +68,7 @@
 
   // JacobianWriter interface.
 
-  // Create evaluate prepareres that point directly into the final jacobian.
+  // Create evaluate preparers that point directly into the final jacobian.
   // This makes the final Write() a nop.
   std::unique_ptr<BlockEvaluatePreparer[]> CreateEvaluatePreparers(
       unsigned num_threads);