Fix example in README.md to compile.
Fix example in README.md to compile.

Fixes #65

subailong/benchmark,eliben/benchmark,fuchsia-mirror/third_party-benchmark,mockingbirdnest/benchmark,eliben/benchmark,mockingbirdnest/benchmark,xlqian/benchmark,disconnect3d/benchmark,efcs/benchmark,disconnect3d/benchmark,xlqian/benchmark,chandlerc/benchmark,everbase/benchmark,gezidan/benchmark,ntx-/benchmark,codygray/benchmark,google/benchmark,nickhutchinson/benchmark-cxx03,codygray/benchmark,LepelTsmok/benchmark,fuchsia-mirror/third_party-benchmark,subailong/benchmark,mockingbirdnest/benchmark,quantumsteve/benchmark,eliben/benchmark,chemhack/benchmark,chemhack/benchmark,subailong/benchmark,xlqian/benchmark,everbase/benchmark,nickhutchinson/benchmark,ntx-/benchmark,Photonomie/benchmark,codygray/benchmark,subailong/benchmark,Photonomie/benchmark,nickhutchinson/benchmark-cxx03,Photonomie/benchmark,nickhutchinson/benchmark,xlqian/benchmark,bowlofstew/benchmark,gezidan/benchmark,efcs/benchmark,LepelTsmok/benchmark,chemhack/benchmark,quantumsteve/benchmark,everbase/benchmark,efcs/benchmark,disconnect3d/benchmark,google/benchmark,Photonomie/benchmark,google/benchmark,quantumsteve/benchmark,quantumsteve/benchmark,chandlerc/benchmark,chemhack/benchmark,fuchsia-mirror/third_party-benchmark,disconnect3d/benchmark,codygray/benchmark,bowlofstew/benchmark,everbase/benchmark,bowlofstew/benchmark,nickhutchinson/benchmark,ntx-/benchmark,efcs/benchmark,gezidan/benchmark,fuchsia-mirror/third_party-benchmark,mockingbirdnest/benchmark,gezidan/benchmark,chandlerc/benchmark,nickhutchinson/benchmark,nickhutchinson/benchmark-cxx03,eliben/benchmark,LepelTsmok/benchmark,bowlofstew/benchmark,ntx-/benchmark,nickhutchinson/benchmark-cxx03,chandlerc/benchmark,LepelTsmok/benchmark