Fix Lua tests

Change-Id: I9ad73317b5c6a7120bd747dedca6331b05a086b0
diff --git a/tests/lua/test_influxdb.lua b/tests/lua/test_influxdb.lua
index 73d650d..ee74476 100644
--- a/tests/lua/test_influxdb.lua
+++ b/tests/lua/test_influxdb.lua
@@ -43,7 +43,7 @@
     end
 
     function TestInfluxDB:test_us_precision_encoder()
-        local encoder = influxdb.new("us")
+        local encoder = influxdb.new("u")
         assertEquals(encoder:encode_datapoint(1e9 * 1000, 'foo', 1), 'foo value=1.000000 1000000000')
     end