Pandas 0.23.4: Memory Error on doing pd.merge() with smallish csv files
#### Code Sample, a copy-pastable example if possible

See gist of code:
https://nbviewer.jupyter.org/gist/pybokeh/434e290a1af3636a3f84097e3aa45a72

#### Problem description

Get memory error - see gist above

#### Expected Output
Not get memory error

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.0.final.0
python-bits: 32
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.23.4
pytest: None
pip: 19.0
setuptools: 39.0.1
Cython: None
numpy: 1.16.0
scipy: 1.2.0
pyarrow: None
xarray: None
IPython: 6.5.0
sphinx: None
patsy: 0.5.0
dateutil: 2.7.3
pytz: 2018.5
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 3.0.0
openpyxl: 2.5.7
xlrd: 1.1.0
xlwt: None
xlsxwriter: None
lxml: 4.2.5
bs4: 4.6.3
html5lib: 1.0.1
sqlalchemy: 1.2.14
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>



I have the csv files that I can email to someone or provided in a different manner.