to_excel function not working as expected
#### Code Sample, a copy-pastable example if possible

to_excel function displays datetime types incorrectly in Excel
before: datetime64[ns] - 2016-09-28 (seconds removed)
after saving in excel file via - to_excel -> shows up as 2016-09-28 00:00:00 in excel (00:00:00 is added for no reason)
#### Expected Output

2016-09-28 in excel
#### output of `pd.show_versions()`
## INSTALLED VERSIONS

commit: None
python: 2.7.10.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.11-23.53.amzn1.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.1
nose: 1.3.0
pip: 8.1.2
setuptools: 12.2
Cython: None
numpy: 1.7.2
scipy: None
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.1
pytz: 2016.4
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.2.0
openpyxl: 2.4.0-b1
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: None
lxml: 3.6.0
bs4: 4.4.1
html5lib: 0.9999999
httplib2: None
apiclient: None
sqlalchemy: 1.0.14
pymysql: None
psycopg2: None
jinja2: 2.7.2
boto: 2.39.0
pandas_datareader: None
