Ensure alphaTest is formatted as a float

src/renderers/webgl/WebGLProgram.js

@@ -438,7 +438,7 @@ function WebGLProgram( renderer, extensions, code, material, shader, parameters
 
 			customDefines,
 
-			parameters.alphaTest ? '#define ALPHATEST ' + parameters.alphaTest : '',
+			parameters.alphaTest ? '#define ALPHATEST ' + parameters.alphaTest + ( parameters.alphaTest % 1 ? '' : '.0' ) : '', // add '.0' if integer
 
 			'#define GAMMA_FACTOR ' + gammaFactorDefine,